libvpx: Pull from upstream

source/libvpx/third_party/libwebm/mkvparser.cpp

+// Copyright (c) 2012 The WebM project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+
+#include "mkvparser.hpp"
+#include <cassert>
+#include <cstring>
+#include <new>
+#include <climits>
+
+#ifdef _MSC_VER
+// Disable MSVC warnings that suggest making code non-portable.
+#pragma warning(disable:4996)
+#endif
+
+mkvparser::IMkvReader::~IMkvReader()
+{
+}
+
+void mkvparser::GetVersion(int& major, int& minor, int& build, int& revision)
+{
+    major = 1;
+    minor = 0;
+    build = 0;
+    revision = 27;
+}
+
+long long mkvparser::ReadUInt(IMkvReader* pReader, long long pos, long& len)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    int status;
+
+//#ifdef _DEBUG
+//    long long total, available;
+//    status = pReader->Length(&total, &available);
+//    assert(status >= 0);
+//    assert((total < 0) || (available <= total));
+//    assert(pos < available);
+//    assert((available - pos) >= 1);  //assume here max u-int len is 8
+//#endif
+
+    len = 1;
+
+    unsigned char b;
+
+    status = pReader->Read(pos, 1, &b);
+
+    if (status < 0)  //error or underflow
+        return status;
+
+    if (status > 0)  //interpreted as "underflow"
+        return E_BUFFER_NOT_FULL;
+
+    if (b == 0)  //we can't handle u-int values larger than 8 bytes
+        return E_FILE_FORMAT_INVALID;
+
+    unsigned char m = 0x80;
+
+    while (!(b & m))
+    {
+        m >>= 1;
+        ++len;
+    }
+
+//#ifdef _DEBUG
+//    assert((available - pos) >= len);
+//#endif
+
+    long long result = b & (~m);
+    ++pos;
+
+    for (int i = 1; i < len; ++i)
+    {
+        status = pReader->Read(pos, 1, &b);
+
+        if (status < 0)
+        {
+            len = 1;
+            return status;
+        }
+
+        if (status > 0)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result <<= 8;
+        result |= b;
+
+        ++pos;
+    }
+
+    return result;
+}
+
+long long mkvparser::GetUIntLength(
+    IMkvReader* pReader,
+    long long pos,
+    long& len)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    long long total, available;
+
+    int status = pReader->Length(&total, &available);
+    assert(status >= 0);
+    assert((total < 0) || (available <= total));
+
+    len = 1;
+
+    if (pos >= available)
+        return pos;  //too few bytes available
+
+    unsigned char b;
+
+    status = pReader->Read(pos, 1, &b);
+
+    if (status < 0)
+        return status;
+
+    assert(status == 0);
+
+    if (b == 0)  //we can't handle u-int values larger than 8 bytes
+        return E_FILE_FORMAT_INVALID;
+
+    unsigned char m = 0x80;
+
+    while (!(b & m))
+    {
+        m >>= 1;
+        ++len;
+    }
+
+    return 0;  //success
+}
+
+
+long long mkvparser::UnserializeUInt(
+    IMkvReader* pReader,
+    long long pos,
+    long long size)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    if ((size <= 0) || (size > 8))
+        return E_FILE_FORMAT_INVALID;
+
+    long long result = 0;
+
+    for (long long i = 0; i < size; ++i)
+    {
+        unsigned char b;
+
+        const long status = pReader->Read(pos, 1, &b);
+
+        if (status < 0)
+            return status;
+
+        result <<= 8;
+        result |= b;
+
+        ++pos;
+    }
+
+    return result;
+}
+
+
+long mkvparser::UnserializeFloat(
+    IMkvReader* pReader,
+    long long pos,
+    long long size_,
+    double& result)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    if ((size_ != 4) && (size_ != 8))
+        return E_FILE_FORMAT_INVALID;
+
+    const long size = static_cast<long>(size_);
+
+    unsigned char buf[8];
+
+    const int status = pReader->Read(pos, size, buf);
+
+    if (status < 0)  //error
+        return status;
+
+    if (size == 4)
+    {
+        union
+        {
+            float f;
+            unsigned long ff;
+        };
+
+        ff = 0;
+
+        for (int i = 0;;)
+        {
+            ff |= buf[i];
+
+            if (++i >= 4)
+                break;
+
+            ff <<= 8;
+        }
+
+        result = f;
+    }
+    else
+    {
+        assert(size == 8);
+
+        union
+        {
+            double d;
+            unsigned long long dd;
+        };
+
+        dd = 0;
+
+        for (int i = 0;;)
+        {
+            dd |= buf[i];
+
+            if (++i >= 8)
+                break;
+
+            dd <<= 8;
+        }
+
+        result = d;
+    }
+
+    return 0;
+}
+
+
+long mkvparser::UnserializeInt(
+    IMkvReader* pReader,
+    long long pos,
+    long size,
+    long long& result)
+{
+    assert(pReader);
+    assert(pos >= 0);
+    assert(size > 0);
+    assert(size <= 8);
+
+    {
+        signed char b;
+
+        const long status = pReader->Read(pos, 1, (unsigned char*)&b);
+
+        if (status < 0)
+            return status;
+
+        result = b;
+
+        ++pos;
+    }
+
+    for (long i = 1; i < size; ++i)
+    {
+        unsigned char b;
+
+        const long status = pReader->Read(pos, 1, &b);
+
+        if (status < 0)
+            return status;
+
+        result <<= 8;
+        result |= b;
+
+        ++pos;
+    }
+
+    return 0;  //success
+}
+
+
+long mkvparser::UnserializeString(
+    IMkvReader* pReader,
+    long long pos,
+    long long size_,
+    char*& str)
+{
+    delete[] str;
+    str = NULL;
+
+    if (size_ >= LONG_MAX)  //we need (size+1) chars
+        return E_FILE_FORMAT_INVALID;
+
+    const long size = static_cast<long>(size_);
+
+    str = new (std::nothrow) char[size+1];
+
+    if (str == NULL)
+        return -1;
+
+    unsigned char* const buf = reinterpret_cast<unsigned char*>(str);
+
+    const long status = pReader->Read(pos, size, buf);
+
+    if (status)
+    {
+        delete[] str;
+        str = NULL;
+
+        return status;
+    }
+
+    str[size] = '\0';
+
+    return 0;  //success
+}
+
+
+long mkvparser::ParseElementHeader(
+    IMkvReader* pReader,
+    long long& pos,
+    long long stop,
+    long long& id,
+    long long& size)
+{
+    if ((stop >= 0) && (pos >= stop))
+        return E_FILE_FORMAT_INVALID;
+
+    long len;
+
+    id = ReadUInt(pReader, pos, len);
+
+    if (id < 0)
+        return E_FILE_FORMAT_INVALID;
+
+    pos += len;  //consume id
+
+    if ((stop >= 0) && (pos >= stop))
+        return E_FILE_FORMAT_INVALID;
+
+    size = ReadUInt(pReader, pos, len);
+
+    if (size < 0)
+        return E_FILE_FORMAT_INVALID;
+
+    pos += len;  //consume length of size
+
+    //pos now designates payload
+
+    if ((stop >= 0) && ((pos + size) > stop))
+        return E_FILE_FORMAT_INVALID;
+
+    return 0;  //success
+}
+
+
+bool mkvparser::Match(
+    IMkvReader* pReader,
+    long long& pos,
+    unsigned long id_,
+    long long& val)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    long long total, available;
+
+    const long status = pReader->Length(&total, &available);
+    assert(status >= 0);
+    assert((total < 0) || (available <= total));
+    if (status < 0)
+        return false;
+
+    long len;
+
+    const long long id = ReadUInt(pReader, pos, len);
+    assert(id >= 0);
+    assert(len > 0);
+    assert(len <= 8);
+    assert((pos + len) <= available);
+
+    if ((unsigned long)id != id_)
+        return false;
+
+    pos += len;  //consume id
+
+    const long long size = ReadUInt(pReader, pos, len);
+    assert(size >= 0);
+    assert(size <= 8);
+    assert(len > 0);
+    assert(len <= 8);
+    assert((pos + len) <= available);
+
+    pos += len;  //consume length of size of payload
+
+    val = UnserializeUInt(pReader, pos, size);
+    assert(val >= 0);
+
+    pos += size;  //consume size of payload
+
+    return true;
+}
+
+bool mkvparser::Match(
+    IMkvReader* pReader,
+    long long& pos,
+    unsigned long id_,
+    unsigned char*& buf,
+    size_t& buflen)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    long long total, available;
+
+    long status = pReader->Length(&total, &available);
+    assert(status >= 0);
+    assert((total < 0) || (available <= total));
+    if (status < 0)
+        return false;
+
+    long len;
+    const long long id = ReadUInt(pReader, pos, len);
+    assert(id >= 0);
+    assert(len > 0);
+    assert(len <= 8);
+    assert((pos + len) <= available);
+
+    if ((unsigned long)id != id_)
+        return false;
+
+    pos += len;  //consume id
+
+    const long long size_ = ReadUInt(pReader, pos, len);
+    assert(size_ >= 0);
+    assert(len > 0);
+    assert(len <= 8);
+    assert((pos + len) <= available);
+
+    pos += len;  //consume length of size of payload
+    assert((pos + size_) <= available);
+
+    const long buflen_ = static_cast<long>(size_);
+
+    buf = new (std::nothrow) unsigned char[buflen_];
+    assert(buf);  //TODO
+
+    status = pReader->Read(pos, buflen_, buf);
+    assert(status == 0);  //TODO
+
+    buflen = buflen_;
+
+    pos += size_;  //consume size of payload
+    return true;
+}
+
+
+namespace mkvparser
+{
+
+EBMLHeader::EBMLHeader() :
+    m_docType(NULL)
+{
+    Init();
+}
+
+EBMLHeader::~EBMLHeader()
+{
+    delete[] m_docType;
+}
+
+void EBMLHeader::Init()
+{
+    m_version = 1;
+    m_readVersion = 1;
+    m_maxIdLength = 4;
+    m_maxSizeLength = 8;
+
+    if (m_docType)
+    {
+        delete[] m_docType;
+        m_docType = NULL;
+    }
+
+    m_docTypeVersion = 1;
+    m_docTypeReadVersion = 1;
+}
+
+long long EBMLHeader::Parse(
+    IMkvReader* pReader,
+    long long& pos)
+{
+    assert(pReader);
+
+    long long total, available;
+
+    long status = pReader->Length(&total, &available);
+
+    if (status < 0)  //error
+        return status;
+
+    pos = 0;
+    long long end = (available >= 1024) ? 1024 : available;
+
+    for (;;)
+    {
+        unsigned char b = 0;
+
+        while (pos < end)
+        {
+            status = pReader->Read(pos, 1, &b);
+
+            if (status < 0)  //error
+                return status;
+
+            if (b == 0x1A)
+                break;
+
+            ++pos;
+        }
+
+        if (b != 0x1A)
+        {
+            if (pos >= 1024)
+                return E_FILE_FORMAT_INVALID;  //don't bother looking anymore
+
+            if ((total >= 0) && ((total - available) < 5))
+                return E_FILE_FORMAT_INVALID;
+
+            return available + 5;  //5 = 4-byte ID + 1st byte of size
+        }
+
+        if ((total >= 0) && ((total - pos) < 5))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((available - pos) < 5)
+            return pos + 5;  //try again later
+
+        long len;
+
+        const long long result = ReadUInt(pReader, pos, len);
+
+        if (result < 0)  //error
+            return result;
+
+        if (result == 0x0A45DFA3)  //EBML Header ID
+        {
+            pos += len;  //consume ID
+            break;
+        }
+
+        ++pos;  //throw away just the 0x1A byte, and try again
+    }
+
+    //pos designates start of size field
+
+    //get length of size field
+
+    long len;
+    long long result = GetUIntLength(pReader, pos, len);
+
+    if (result < 0)  //error
+        return result;
+
+    if (result > 0)  //need more data
+        return result;
+
+    assert(len > 0);
+    assert(len <= 8);
+
+    if ((total >= 0) && ((total -  pos) < len))
+        return E_FILE_FORMAT_INVALID;
+
+    if ((available - pos) < len)
+        return pos + len;  //try again later
+
+    //get the EBML header size
+
+    result = ReadUInt(pReader, pos, len);
+
+    if (result < 0)  //error
+        return result;
+
+    pos += len;  //consume size field
+
+    //pos now designates start of payload
+
+    if ((total >= 0) && ((total - pos) < result))
+        return E_FILE_FORMAT_INVALID;
+
+    if ((available - pos) < result)
+        return pos + result;
+
+    end = pos + result;
+
+    Init();
+
+    while (pos < end)
+    {
+        long long id, size;
+
+        status = ParseElementHeader(
+                    pReader,
+                    pos,
+                    end,
+                    id,
+                    size);
+
+        if (status < 0) //error
+            return status;
+
+        if (size == 0)  //weird
+            return E_FILE_FORMAT_INVALID;
+
+        if (id == 0x0286)  //version
+        {
+            m_version = UnserializeUInt(pReader, pos, size);
+
+            if (m_version <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x02F7)  //read version
+        {
+            m_readVersion = UnserializeUInt(pReader, pos, size);
+
+            if (m_readVersion <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x02F2)  //max id length
+        {
+            m_maxIdLength = UnserializeUInt(pReader, pos, size);
+
+            if (m_maxIdLength <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x02F3)  //max size length
+        {
+            m_maxSizeLength = UnserializeUInt(pReader, pos, size);
+
+            if (m_maxSizeLength <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x0282)  //doctype
+        {
+            if (m_docType)
+                return E_FILE_FORMAT_INVALID;
+
+            status = UnserializeString(pReader, pos, size, m_docType);
+
+            if (status)  //error
+                return status;
+        }
+        else if (id == 0x0287)  //doctype version
+        {
+            m_docTypeVersion = UnserializeUInt(pReader, pos, size);
+
+            if (m_docTypeVersion <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x0285)  //doctype read version
+        {
+            m_docTypeReadVersion = UnserializeUInt(pReader, pos, size);
+
+            if (m_docTypeReadVersion <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+
+        pos += size;
+    }
+
+    assert(pos == end);
+    return 0;
+}
+
+
+Segment::Segment(
+    IMkvReader* pReader,
+    long long elem_start,
+    //long long elem_size,
+    long long start,
+    long long size) :
+    m_pReader(pReader),
+    m_element_start(elem_start),
+    //m_element_size(elem_size),
+    m_start(start),
+    m_size(size),
+    m_pos(start),
+    m_pUnknownSize(0),
+    m_pSeekHead(NULL),
+    m_pInfo(NULL),
+    m_pTracks(NULL),
+    m_pCues(NULL),
+    m_pChapters(NULL),
+    m_clusters(NULL),
+    m_clusterCount(0),
+    m_clusterPreloadCount(0),
+    m_clusterSize(0)
+{
+}
+
+
+Segment::~Segment()
+{
+    const long count = m_clusterCount + m_clusterPreloadCount;
+
+    Cluster** i = m_clusters;
+    Cluster** j = m_clusters + count;
+
+    while (i != j)
+    {
+        Cluster* const p = *i++;
+        assert(p);
+
+        delete p;
+    }
+
+    delete[] m_clusters;
+
+    delete m_pTracks;
+    delete m_pInfo;
+    delete m_pCues;
+    delete m_pChapters;
+    delete m_pSeekHead;
+}
+
+
+long long Segment::CreateInstance(
+    IMkvReader* pReader,
+    long long pos,
+    Segment*& pSegment)
+{
+    assert(pReader);
+    assert(pos >= 0);
+
+    pSegment = NULL;
+
+    long long total, available;
+
+    const long status = pReader->Length(&total, &available);
+
+    if (status < 0) //error
+        return status;
+
+    if (available < 0)
+        return -1;
+
+    if ((total >= 0) && (available > total))
+        return -1;
+
+    //I would assume that in practice this loop would execute
+    //exactly once, but we allow for other elements (e.g. Void)
+    //to immediately follow the EBML header.  This is fine for
+    //the source filter case (since the entire file is available),
+    //but in the splitter case over a network we should probably
+    //just give up early.  We could for example decide only to
+    //execute this loop a maximum of, say, 10 times.
+    //TODO:
+    //There is an implied "give up early" by only parsing up
+    //to the available limit.  We do do that, but only if the
+    //total file size is unknown.  We could decide to always
+    //use what's available as our limit (irrespective of whether
+    //we happen to know the total file length).  This would have
+    //as its sense "parse this much of the file before giving up",
+    //which a slightly different sense from "try to parse up to
+    //10 EMBL elements before giving up".
+
+    for (;;)
+    {
+        if ((total >= 0) && (pos >= total))
+            return E_FILE_FORMAT_INVALID;
+
+        //Read ID
+        long len;
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result)  //error, or too few available bytes
+            return result;
+
+        if ((total >= 0) && ((pos + len) > total))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > available)
+            return pos + len;
+
+        const long long idpos = pos;
+        const long long id = ReadUInt(pReader, pos, len);
+
+        if (id < 0)  //error
+            return id;
+
+        pos += len;  //consume ID
+
+        //Read Size
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result)  //error, or too few available bytes
+            return result;
+
+        if ((total >= 0) && ((pos + len) > total))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > available)
+            return pos + len;
+
+        long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return size;
+
+        pos += len;  //consume length of size of element
+
+        //Pos now points to start of payload
+
+        //Handle "unknown size" for live streaming of webm files.
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (id == 0x08538067)  //Segment ID
+        {
+            if (size == unknown_size)
+                size = -1;
+
+            else if (total < 0)
+                size = -1;
+
+            else if ((pos + size) > total)
+                size = -1;
+
+            pSegment = new (std::nothrow) Segment(
+                                            pReader,
+                                            idpos,
+                                            //elem_size
+                                            pos,
+                                            size);
+
+            if (pSegment == 0)
+                return -1;  //generic error
+
+            return 0;    //success
+        }
+
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((total >= 0) && ((pos + size) > total))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + size) > available)
+            return pos + size;
+
+        pos += size;  //consume payload
+    }
+}
+
+
+long long Segment::ParseHeaders()
+{
+    //Outermost (level 0) segment object has been constructed,
+    //and pos designates start of payload.  We need to find the
+    //inner (level 1) elements.
+    long long total, available;
+
+    const int status = m_pReader->Length(&total, &available);
+
+    if (status < 0) //error
+        return status;
+
+    assert((total < 0) || (available <= total));
+
+    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
+    assert((segment_stop < 0) || (total < 0) || (segment_stop <= total));
+    assert((segment_stop < 0) || (m_pos <= segment_stop));
+
+    for (;;)
+    {
+        if ((total >= 0) && (m_pos >= total))
+            break;
+
+        if ((segment_stop >= 0) && (m_pos >= segment_stop))
+            break;
+
+        long long pos = m_pos;
+        const long long element_start = pos;
+
+        if ((pos + 1) > available)
+            return (pos + 1);
+
+        long len;
+        long long result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return result;
+
+        if (result > 0)  //underflow (weird)
+            return (pos + 1);
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > available)
+            return pos + len;
+
+        const long long idpos = pos;
+        const long long id = ReadUInt(m_pReader, idpos, len);
+
+        if (id < 0)  //error
+            return id;
+
+        if (id == 0x0F43B675)  //Cluster ID
+            break;
+
+        pos += len;  //consume ID
+
+        if ((pos + 1) > available)
+            return (pos + 1);
+
+        //Read Size
+        result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return result;
+
+        if (result > 0)  //underflow (weird)
+            return (pos + 1);
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > available)
+            return pos + len;
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+
+        if (size < 0)  //error
+            return size;
+
+        pos += len;  //consume length of size of element
+
+        const long long element_size = size + pos - element_start;
+
+        //Pos now points to start of payload
+
+        if ((segment_stop >= 0) && ((pos + size) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        //We read EBML elements either in total or nothing at all.
+
+        if ((pos + size) > available)
+            return pos + size;
+
+        if (id == 0x0549A966)  //Segment Info ID
+        {
+            if (m_pInfo)
+                return E_FILE_FORMAT_INVALID;
+
+            m_pInfo = new (std::nothrow) SegmentInfo(
+                                          this,
+                                          pos,
+                                          size,
+                                          element_start,
+                                          element_size);
+
+            if (m_pInfo == NULL)
+                return -1;
+
+            const long status = m_pInfo->Parse();
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x0654AE6B)  //Tracks ID
+        {
+            if (m_pTracks)
+                return E_FILE_FORMAT_INVALID;
+
+            m_pTracks = new (std::nothrow) Tracks(this,
+                                                  pos,
+                                                  size,
+                                                  element_start,
+                                                  element_size);
+
+            if (m_pTracks == NULL)
+                return -1;
+
+            const long status = m_pTracks->Parse();
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x0C53BB6B)  //Cues ID
+        {
+            if (m_pCues == NULL)
+            {
+                m_pCues = new (std::nothrow) Cues(
+                                                this,
+                                                pos,
+                                                size,
+                                                element_start,
+                                                element_size);
+
+                if (m_pCues == NULL)
+                    return -1;
+            }
+        }
+        else if (id == 0x014D9B74)  //SeekHead ID
+        {
+            if (m_pSeekHead == NULL)
+            {
+                m_pSeekHead = new (std::nothrow) SeekHead(
+                                                    this,
+                                                    pos,
+                                                    size,
+                                                    element_start,
+                                                    element_size);
+
+                if (m_pSeekHead == NULL)
+                    return -1;
+
+                const long status = m_pSeekHead->Parse();
+
+                if (status)
+                    return status;
+            }
+        }
+        else if (id == 0x0043A770)  //Chapters ID
+        {
+            if (m_pChapters == NULL)
+            {
+                m_pChapters = new (std::nothrow) Chapters(
+                                this,
+                                pos,
+                                size,
+                                element_start,
+                                element_size);
+
+                if (m_pChapters == NULL)
+                  return -1;
+
+                const long status = m_pChapters->Parse();
+
+                if (status)
+                  return status;
+            }
+        }
+
+        m_pos = pos + size;  //consume payload
+    }
+
+    assert((segment_stop < 0) || (m_pos <= segment_stop));
+
+    if (m_pInfo == NULL)  //TODO: liberalize this behavior
+        return E_FILE_FORMAT_INVALID;
+
+    if (m_pTracks == NULL)
+        return E_FILE_FORMAT_INVALID;
+
+    return 0;  //success
+}
+
+
+long Segment::LoadCluster(
+    long long& pos,
+    long& len)
+{
+    for (;;)
+    {
+        const long result = DoLoadCluster(pos, len);
+
+        if (result <= 1)
+            return result;
+    }
+}
+
+
+long Segment::DoLoadCluster(
+    long long& pos,
+    long& len)
+{
+    if (m_pos < 0)
+        return DoLoadClusterUnknownSize(pos, len);
+
+    long long total, avail;
+
+    long status = m_pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
+
+    long long cluster_off = -1;   //offset relative to start of segment
+    long long cluster_size = -1;  //size of cluster payload
+
+    for (;;)
+    {
+        if ((total >= 0) && (m_pos >= total))
+            return 1;  //no more clusters
+
+        if ((segment_stop >= 0) && (m_pos >= segment_stop))
+            return 1;  //no more clusters
+
+        pos = m_pos;
+
+        //Read ID
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long idpos = pos;
+        const long long id = ReadUInt(m_pReader, idpos, len);
+
+        if (id < 0)  //error (or underflow)
+            return static_cast<long>(id);
+
+        pos += len;  //consume ID
+
+        //Read Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        pos += len;  //consume length of size of element
+
+        //pos now points to start of payload
+
+        if (size == 0)  //weird
+        {
+            m_pos = pos;
+            continue;
+        }
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+#if 0  //we must handle this to support live webm
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;  //TODO: allow this
+#endif
+
+        if ((segment_stop >= 0) &&
+            (size != unknown_size) &&
+            ((pos + size) > segment_stop))
+        {
+            return E_FILE_FORMAT_INVALID;
+        }
+
+#if 0  //commented-out, to support incremental cluster parsing
+        len = static_cast<long>(size);
+
+        if ((pos + size) > avail)
+            return E_BUFFER_NOT_FULL;
+#endif
+
+        if (id == 0x0C53BB6B)  //Cues ID
+        {
+            if (size == unknown_size)
+                return E_FILE_FORMAT_INVALID;  //TODO: liberalize
+
+            if (m_pCues == NULL)
+            {
+                const long long element_size = (pos - idpos) + size;
+
+                m_pCues = new Cues(this,
+                                   pos,
+                                   size,
+                                   idpos,
+                                   element_size);
+                assert(m_pCues);  //TODO
+            }
+
+            m_pos = pos + size;  //consume payload
+            continue;
+        }
+
+        if (id != 0x0F43B675)  //Cluster ID
+        {
+            if (size == unknown_size)
+                return E_FILE_FORMAT_INVALID;  //TODO: liberalize
+
+            m_pos = pos + size;  //consume payload
+            continue;
+        }
+
+        //We have a cluster.
+
+        cluster_off = idpos - m_start;  //relative pos
+
+        if (size != unknown_size)
+            cluster_size = size;
+
+        break;
+    }
+
+    assert(cluster_off >= 0);  //have cluster
+
+    long long pos_;
+    long len_;
+
+    status = Cluster::HasBlockEntries(this, cluster_off, pos_, len_);
+
+    if (status < 0) //error, or underflow
+    {
+        pos = pos_;
+        len = len_;
+
+        return status;
+    }
+
+    //status == 0 means "no block entries found"
+    //status > 0 means "found at least one block entry"
+
+    //TODO:
+    //The issue here is that the segment increments its own
+    //pos ptr past the most recent cluster parsed, and then
+    //starts from there to parse the next cluster.  If we
+    //don't know the size of the current cluster, then we
+    //must either parse its payload (as we do below), looking
+    //for the cluster (or cues) ID to terminate the parse.
+    //This isn't really what we want: rather, we really need
+    //a way to create the curr cluster object immediately.
+    //The pity is that cluster::parse can determine its own
+    //boundary, and we largely duplicate that same logic here.
+    //
+    //Maybe we need to get rid of our look-ahead preloading
+    //in source::parse???
+    //
+    //As we're parsing the blocks in the curr cluster
+    //(in cluster::parse), we should have some way to signal
+    //to the segment that we have determined the boundary,
+    //so it can adjust its own segment::m_pos member.
+    //
+    //The problem is that we're asserting in asyncreadinit,
+    //because we adjust the pos down to the curr seek pos,
+    //and the resulting adjusted len is > 2GB.  I'm suspicious
+    //that this is even correct, but even if it is, we can't
+    //be loading that much data in the cache anyway.
+
+    const long idx = m_clusterCount;
+
+    if (m_clusterPreloadCount > 0)
+    {
+        assert(idx < m_clusterSize);
+
+        Cluster* const pCluster = m_clusters[idx];
+        assert(pCluster);
+        assert(pCluster->m_index < 0);
+
+        const long long off = pCluster->GetPosition();
+        assert(off >= 0);
+
+        if (off == cluster_off)  //preloaded already
+        {
+            if (status == 0)  //no entries found
+                return E_FILE_FORMAT_INVALID;
+
+            if (cluster_size >= 0)
+                pos += cluster_size;
+            else
+            {
+                const long long element_size = pCluster->GetElementSize();
+
+                if (element_size <= 0)
+                    return E_FILE_FORMAT_INVALID;  //TODO: handle this case
+
+                pos = pCluster->m_element_start + element_size;
+            }
+
+            pCluster->m_index = idx;  //move from preloaded to loaded
+            ++m_clusterCount;
+            --m_clusterPreloadCount;
+
+            m_pos = pos;  //consume payload
+            assert((segment_stop < 0) || (m_pos <= segment_stop));
+
+            return 0;  //success
+        }
+    }
+
+    if (status == 0)  //no entries found
+    {
+        if (cluster_size < 0)
+            return E_FILE_FORMAT_INVALID;  //TODO: handle this
+
+        pos += cluster_size;
+
+        if ((total >= 0) && (pos >= total))
+        {
+            m_pos = total;
+            return 1;  //no more clusters
+        }
+
+        if ((segment_stop >= 0) && (pos >= segment_stop))
+        {
+            m_pos = segment_stop;
+            return 1;  //no more clusters
+        }
+
+        m_pos = pos;
+        return 2;  //try again
+    }
+
+    //status > 0 means we have an entry
+
+    Cluster* const pCluster = Cluster::Create(this,
+                                              idx,
+                                              cluster_off);
+                                              //element_size);
+    assert(pCluster);
+
+    AppendCluster(pCluster);
+    assert(m_clusters);
+    assert(idx < m_clusterSize);
+    assert(m_clusters[idx] == pCluster);
+
+    if (cluster_size >= 0)
+    {
+        pos += cluster_size;
+
+        m_pos = pos;
+        assert((segment_stop < 0) || (m_pos <= segment_stop));
+
+        return 0;
+    }
+
+    m_pUnknownSize = pCluster;
+    m_pos = -pos;
+
+    return 0;  //partial success, since we have a new cluster
+
+    //status == 0 means "no block entries found"
+
+    //pos designates start of payload
+    //m_pos has NOT been adjusted yet (in case we need to come back here)
+
+#if 0
+
+    if (cluster_size < 0)  //unknown size
+    {
+        const long long payload_pos = pos;  //absolute pos of cluster payload
+
+        for (;;)  //determine cluster size
+        {
+            if ((total >= 0) && (pos >= total))
+                break;
+
+            if ((segment_stop >= 0) && (pos >= segment_stop))
+                break;  //no more clusters
+
+            //Read ID
+
+            if ((pos + 1) > avail)
+            {
+                len = 1;
+                return E_BUFFER_NOT_FULL;
+            }
+
+            long long result = GetUIntLength(m_pReader, pos, len);
+
+            if (result < 0)  //error
+                return static_cast<long>(result);
+
+            if (result > 0)  //weird
+                return E_BUFFER_NOT_FULL;
+
+            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+                return E_FILE_FORMAT_INVALID;
+
+            if ((pos + len) > avail)
+                return E_BUFFER_NOT_FULL;
+
+            const long long idpos = pos;
+            const long long id = ReadUInt(m_pReader, idpos, len);
+
+            if (id < 0)  //error (or underflow)
+                return static_cast<long>(id);
+
+            //This is the distinguished set of ID's we use to determine
+            //that we have exhausted the sub-element's inside the cluster
+            //whose ID we parsed earlier.
+
+            if (id == 0x0F43B675)  //Cluster ID
+                break;
+
+            if (id == 0x0C53BB6B)  //Cues ID
+                break;
+
+            switch (id)
+            {
+                case 0x20:  //BlockGroup
+                case 0x23:  //Simple Block
+                case 0x67:  //TimeCode
+                case 0x2B:  //PrevSize
+                    break;
+
+                default:
+                    assert(false);
+                    break;
+            }
+
+            pos += len;  //consume ID (of sub-element)
+
+            //Read Size
+
+            if ((pos + 1) > avail)
+            {
+                len = 1;
+                return E_BUFFER_NOT_FULL;
+            }
+
+            result = GetUIntLength(m_pReader, pos, len);
+
+            if (result < 0)  //error
+                return static_cast<long>(result);
+
+            if (result > 0)  //weird
+                return E_BUFFER_NOT_FULL;
+
+            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+                return E_FILE_FORMAT_INVALID;
+
+            if ((pos + len) > avail)
+                return E_BUFFER_NOT_FULL;
+
+            const long long size = ReadUInt(m_pReader, pos, len);
+
+            if (size < 0)  //error
+                return static_cast<long>(size);
+
+            pos += len;  //consume size field of element
+
+            //pos now points to start of sub-element's payload
+
+            if (size == 0)  //weird
+                continue;
+
+            const long long unknown_size = (1LL << (7 * len)) - 1;
+
+            if (size == unknown_size)
+                return E_FILE_FORMAT_INVALID;  //not allowed for sub-elements
+
+            if ((segment_stop >= 0) && ((pos + size) > segment_stop))  //weird
+                return E_FILE_FORMAT_INVALID;
+
+            pos += size;  //consume payload of sub-element
+            assert((segment_stop < 0) || (pos <= segment_stop));
+        }  //determine cluster size
+
+        cluster_size = pos - payload_pos;
+        assert(cluster_size >= 0);
+
+        pos = payload_pos;  //reset and re-parse original cluster
+    }
+
+    if (m_clusterPreloadCount > 0)
+    {
+        assert(idx < m_clusterSize);
+
+        Cluster* const pCluster = m_clusters[idx];
+        assert(pCluster);
+        assert(pCluster->m_index < 0);
+
+        const long long off = pCluster->GetPosition();
+        assert(off >= 0);
+
+        if (off == cluster_off)  //preloaded already
+            return E_FILE_FORMAT_INVALID;  //subtle
+    }
+
+    m_pos = pos + cluster_size;  //consume payload
+    assert((segment_stop < 0) || (m_pos <= segment_stop));
+
+    return 2;     //try to find another cluster
+
+#endif
+
+}
+
+
+long Segment::DoLoadClusterUnknownSize(
+    long long& pos,
+    long& len)
+{
+    assert(m_pos < 0);
+    assert(m_pUnknownSize);
+
+#if 0
+    assert(m_pUnknownSize->GetElementSize() < 0);  //TODO: verify this
+
+    const long long element_start = m_pUnknownSize->m_element_start;
+
+    pos = -m_pos;
+    assert(pos > element_start);
+
+    //We have already consumed the (cluster) ID and size fields.
+    //We just need to consume the blocks and other sub-elements
+    //of this cluster, until we discover the boundary.
+
+    long long total, avail;
+
+    long status = m_pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
+
+    long long element_size = -1;
+
+    for (;;)  //determine cluster size
+    {
+        if ((total >= 0) && (pos >= total))
+        {
+            element_size = total - element_start;
+            assert(element_size > 0);
+
+            break;
+        }
+
+        if ((segment_stop >= 0) && (pos >= segment_stop))
+        {
+            element_size = segment_stop - element_start;
+            assert(element_size > 0);
+
+            break;
+        }
+
+        //Read ID
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long idpos = pos;
+        const long long id = ReadUInt(m_pReader, idpos, len);
+
+        if (id < 0)  //error (or underflow)
+            return static_cast<long>(id);
+
+        //This is the distinguished set of ID's we use to determine
+        //that we have exhausted the sub-element's inside the cluster
+        //whose ID we parsed earlier.
+
+        if ((id == 0x0F43B675) || (id == 0x0C53BB6B)) //Cluster ID or Cues ID
+        {
+            element_size = pos - element_start;
+            assert(element_size > 0);
+
+            break;
+        }
+
+#ifdef _DEBUG
+        switch (id)
+        {
+            case 0x20:  //BlockGroup
+            case 0x23:  //Simple Block
+            case 0x67:  //TimeCode
+            case 0x2B:  //PrevSize
+                break;
+
+            default:
+                assert(false);
+                break;
+        }
+#endif
+
+        pos += len;  //consume ID (of sub-element)
+
+        //Read Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        pos += len;  //consume size field of element
+
+        //pos now points to start of sub-element's payload
+
+        if (size == 0)  //weird
+            continue;
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;  //not allowed for sub-elements
+
+        if ((segment_stop >= 0) && ((pos + size) > segment_stop))  //weird
+            return E_FILE_FORMAT_INVALID;
+
+        pos += size;  //consume payload of sub-element
+        assert((segment_stop < 0) || (pos <= segment_stop));
+    }  //determine cluster size
+
+    assert(element_size >= 0);
+
+    m_pos = element_start + element_size;
+    m_pUnknownSize = 0;
+
+    return 2;  //continue parsing
+#else
+    const long status = m_pUnknownSize->Parse(pos, len);
+
+    if (status < 0)  //error or underflow
+        return status;
+
+    if (status == 0)  //parsed a block
+        return 2;     //continue parsing
+
+    assert(status > 0);   //nothing left to parse of this cluster
+
+    const long long start = m_pUnknownSize->m_element_start;
+
+    const long long size = m_pUnknownSize->GetElementSize();
+    assert(size >= 0);
+
+    pos = start + size;
+    m_pos = pos;
+
+    m_pUnknownSize = 0;
+
+    return 2;  //continue parsing
+#endif
+}
+
+
+void Segment::AppendCluster(Cluster* pCluster)
+{
+    assert(pCluster);
+    assert(pCluster->m_index >= 0);
+
+    const long count = m_clusterCount + m_clusterPreloadCount;
+
+    long& size = m_clusterSize;
+    assert(size >= count);
+
+    const long idx = pCluster->m_index;
+    assert(idx == m_clusterCount);
+
+    if (count >= size)
+    {
+        const long n = (size <= 0) ? 2048 : 2*size;
+
+        Cluster** const qq = new Cluster*[n];
+        Cluster** q = qq;
+
+        Cluster** p = m_clusters;
+        Cluster** const pp = p + count;
+
+        while (p != pp)
+            *q++ = *p++;
+
+        delete[] m_clusters;
+
+        m_clusters = qq;
+        size = n;
+    }
+
+    if (m_clusterPreloadCount > 0)
+    {
+        assert(m_clusters);
+
+        Cluster** const p = m_clusters + m_clusterCount;
+        assert(*p);
+        assert((*p)->m_index < 0);
+
+        Cluster** q = p + m_clusterPreloadCount;
+        assert(q < (m_clusters + size));
+
+        for (;;)
+        {
+            Cluster** const qq = q - 1;
+            assert((*qq)->m_index < 0);
+
+            *q = *qq;
+            q = qq;
+
+            if (q == p)
+                break;
+        }
+    }
+
+    m_clusters[idx] = pCluster;
+    ++m_clusterCount;
+}
+
+
+void Segment::PreloadCluster(Cluster* pCluster, ptrdiff_t idx)
+{
+    assert(pCluster);
+    assert(pCluster->m_index < 0);
+    assert(idx >= m_clusterCount);
+
+    const long count = m_clusterCount + m_clusterPreloadCount;
+
+    long& size = m_clusterSize;
+    assert(size >= count);
+
+    if (count >= size)
+    {
+        const long n = (size <= 0) ? 2048 : 2*size;
+
+        Cluster** const qq = new Cluster*[n];
+        Cluster** q = qq;
+
+        Cluster** p = m_clusters;
+        Cluster** const pp = p + count;
+
+        while (p != pp)
+            *q++ = *p++;
+
+        delete[] m_clusters;
+
+        m_clusters = qq;
+        size = n;
+    }
+
+    assert(m_clusters);
+
+    Cluster** const p = m_clusters + idx;
+
+    Cluster** q = m_clusters + count;
+    assert(q >= p);
+    assert(q < (m_clusters + size));
+
+    while (q > p)
+    {
+        Cluster** const qq = q - 1;
+        assert((*qq)->m_index < 0);
+
+        *q = *qq;
+        q = qq;
+    }
+
+    m_clusters[idx] = pCluster;
+    ++m_clusterPreloadCount;
+}
+
+
+long Segment::Load()
+{
+    assert(m_clusters == NULL);
+    assert(m_clusterSize == 0);
+    assert(m_clusterCount == 0);
+    //assert(m_size >= 0);
+
+    //Outermost (level 0) segment object has been constructed,
+    //and pos designates start of payload.  We need to find the
+    //inner (level 1) elements.
+
+    const long long header_status = ParseHeaders();
+
+    if (header_status < 0)  //error
+        return static_cast<long>(header_status);
+
+    if (header_status > 0)  //underflow
+        return E_BUFFER_NOT_FULL;
+
+    assert(m_pInfo);
+    assert(m_pTracks);
+
+    for (;;)
+    {
+        const int status = LoadCluster();
+
+        if (status < 0)  //error
+            return status;
+
+        if (status >= 1)  //no more clusters
+            return 0;
+    }
+}
+
+
+SeekHead::SeekHead(
+    Segment* pSegment,
+    long long start,
+    long long size_,
+    long long element_start,
+    long long element_size) :
+    m_pSegment(pSegment),
+    m_start(start),
+    m_size(size_),
+    m_element_start(element_start),
+    m_element_size(element_size),
+    m_entries(0),
+    m_entry_count(0),
+    m_void_elements(0),
+    m_void_element_count(0)
+{
+}
+
+
+SeekHead::~SeekHead()
+{
+    delete[] m_entries;
+    delete[] m_void_elements;
+}
+
+
+long SeekHead::Parse()
+{
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long pos = m_start;
+    const long long stop = m_start + m_size;
+
+    //first count the seek head entries
+
+    int entry_count = 0;
+    int void_element_count = 0;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (id == 0x0DBB)  //SeekEntry ID
+            ++entry_count;
+        else if (id == 0x6C)  //Void ID
+            ++void_element_count;
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    m_entries = new (std::nothrow) Entry[entry_count];
+
+    if (m_entries == NULL)
+        return -1;
+
+    m_void_elements = new (std::nothrow) VoidElement[void_element_count];
+
+    if (m_void_elements == NULL)
+        return -1;
+
+    //now parse the entries and void elements
+
+    Entry* pEntry = m_entries;
+    VoidElement* pVoidElement = m_void_elements;
+
+    pos = m_start;
+
+    while (pos < stop)
+    {
+        const long long idpos = pos;
+
+        long long id, size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (id == 0x0DBB)  //SeekEntry ID
+        {
+            if (ParseEntry(pReader, pos, size, pEntry))
+            {
+                Entry& e = *pEntry++;
+
+                e.element_start = idpos;
+                e.element_size = (pos + size) - idpos;
+            }
+        }
+        else if (id == 0x6C)  //Void ID
+        {
+            VoidElement& e = *pVoidElement++;
+
+            e.element_start = idpos;
+            e.element_size = (pos + size) - idpos;
+        }
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    ptrdiff_t count_ = ptrdiff_t(pEntry - m_entries);
+    assert(count_ >= 0);
+    assert(count_ <= entry_count);
+
+    m_entry_count = static_cast<int>(count_);
+
+    count_ = ptrdiff_t(pVoidElement - m_void_elements);
+    assert(count_ >= 0);
+    assert(count_ <= void_element_count);
+
+    m_void_element_count = static_cast<int>(count_);
+
+    return 0;
+}
+
+
+int SeekHead::GetCount() const
+{
+    return m_entry_count;
+}
+
+const SeekHead::Entry* SeekHead::GetEntry(int idx) const
+{
+    if (idx < 0)
+        return 0;
+
+    if (idx >= m_entry_count)
+        return 0;
+
+    return m_entries + idx;
+}
+
+int SeekHead::GetVoidElementCount() const
+{
+    return m_void_element_count;
+}
+
+const SeekHead::VoidElement* SeekHead::GetVoidElement(int idx) const
+{
+    if (idx < 0)
+        return 0;
+
+    if (idx >= m_void_element_count)
+        return 0;
+
+    return m_void_elements + idx;
+}
+
+
+#if 0
+void Segment::ParseCues(long long off)
+{
+    if (m_pCues)
+        return;
+
+    //odbgstream os;
+    //os << "Segment::ParseCues (begin)" << endl;
+
+    long long pos = m_start + off;
+    const long long element_start = pos;
+    const long long stop = m_start + m_size;
+
+    long len;
+
+    long long result = GetUIntLength(m_pReader, pos, len);
+    assert(result == 0);
+    assert((pos + len) <= stop);
+
+    const long long idpos = pos;
+
+    const long long id = ReadUInt(m_pReader, idpos, len);
+    assert(id == 0x0C53BB6B);  //Cues ID
+
+    pos += len;  //consume ID
+    assert(pos < stop);
+
+    //Read Size
+
+    result = GetUIntLength(m_pReader, pos, len);
+    assert(result == 0);
+    assert((pos + len) <= stop);
+
+    const long long size = ReadUInt(m_pReader, pos, len);
+    assert(size >= 0);
+
+    pos += len;  //consume length of size of element
+    assert((pos + size) <= stop);
+
+    const long long element_size = size + pos - element_start;
+
+    //Pos now points to start of payload
+
+    m_pCues = new Cues(this, pos, size, element_start, element_size);
+    assert(m_pCues);  //TODO
+
+    //os << "Segment::ParseCues (end)" << endl;
+}
+#else
+long Segment::ParseCues(
+    long long off,
+    long long& pos,
+    long& len)
+{
+    if (m_pCues)
+        return 0;  //success
+
+    if (off < 0)
+        return -1;
+
+    long long total, avail;
+
+    const int status = m_pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    pos = m_start + off;
+
+    if ((total < 0) || (pos >= total))
+        return 1;  //don't bother parsing cues
+
+    const long long element_start = pos;
+    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
+
+    if ((pos + 1) > avail)
+    {
+        len = 1;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    long long result = GetUIntLength(m_pReader, pos, len);
+
+    if (result < 0)  //error
+        return static_cast<long>(result);
+
+    if (result > 0) //underflow (weird)
+    {
+        len = 1;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+        return E_FILE_FORMAT_INVALID;
+
+    if ((pos + len) > avail)
+        return E_BUFFER_NOT_FULL;
+
+    const long long idpos = pos;
+
+    const long long id = ReadUInt(m_pReader, idpos, len);
+
+    if (id != 0x0C53BB6B)  //Cues ID
+        return E_FILE_FORMAT_INVALID;
+
+    pos += len;  //consume ID
+    assert((segment_stop < 0) || (pos <= segment_stop));
+
+    //Read Size
+
+    if ((pos + 1) > avail)
+    {
+        len = 1;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    result = GetUIntLength(m_pReader, pos, len);
+
+    if (result < 0)  //error
+        return static_cast<long>(result);
+
+    if (result > 0) //underflow (weird)
+    {
+        len = 1;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+        return E_FILE_FORMAT_INVALID;
+
+    if ((pos + len) > avail)
+        return E_BUFFER_NOT_FULL;
+
+    const long long size = ReadUInt(m_pReader, pos, len);
+
+    if (size < 0)  //error
+        return static_cast<long>(size);
+
+    if (size == 0)  //weird, although technically not illegal
+        return 1;   //done
+
+    pos += len;  //consume length of size of element
+    assert((segment_stop < 0) || (pos <= segment_stop));
+
+    //Pos now points to start of payload
+
+    const long long element_stop = pos + size;
+
+    if ((segment_stop >= 0) && (element_stop > segment_stop))
+        return E_FILE_FORMAT_INVALID;
+
+    if ((total >= 0) && (element_stop > total))
+        return 1;  //don't bother parsing anymore
+
+    len = static_cast<long>(size);
+
+    if (element_stop > avail)
+        return E_BUFFER_NOT_FULL;
+
+    const long long element_size = element_stop - element_start;
+
+    m_pCues = new (std::nothrow) Cues(
+                                    this,
+                                    pos,
+                                    size,
+                                    element_start,
+                                    element_size);
+    assert(m_pCues);  //TODO
+
+    return 0;  //success
+}
+#endif
+
+
+#if 0
+void Segment::ParseSeekEntry(
+    long long start,
+    long long size_)
+{
+    long long pos = start;
+
+    const long long stop = start + size_;
+
+    long len;
+
+    const long long seekIdId = ReadUInt(m_pReader, pos, len);
+    //seekIdId;
+    assert(seekIdId == 0x13AB);  //SeekID ID
+    assert((pos + len) <= stop);
+
+    pos += len;  //consume id
+
+    const long long seekIdSize = ReadUInt(m_pReader, pos, len);
+    assert(seekIdSize >= 0);
+    assert((pos + len) <= stop);
+
+    pos += len;  //consume size
+
+    const long long seekId = ReadUInt(m_pReader, pos, len);  //payload
+    assert(seekId >= 0);
+    assert(len == seekIdSize);
+    assert((pos + len) <= stop);
+
+    pos += seekIdSize;  //consume payload
+
+    const long long seekPosId = ReadUInt(m_pReader, pos, len);
+    //seekPosId;
+    assert(seekPosId == 0x13AC);  //SeekPos ID
+    assert((pos + len) <= stop);
+
+    pos += len;  //consume id
+
+    const long long seekPosSize = ReadUInt(m_pReader, pos, len);
+    assert(seekPosSize >= 0);
+    assert((pos + len) <= stop);
+
+    pos += len;  //consume size
+    assert((pos + seekPosSize) <= stop);
+
+    const long long seekOff = UnserializeUInt(m_pReader, pos, seekPosSize);
+    assert(seekOff >= 0);
+    assert(seekOff < m_size);
+
+    pos += seekPosSize;  //consume payload
+    assert(pos == stop);
+
+    const long long seekPos = m_start + seekOff;
+    assert(seekPos < (m_start + m_size));
+
+    if (seekId == 0x0C53BB6B)  //Cues ID
+        ParseCues(seekOff);
+}
+#else
+bool SeekHead::ParseEntry(
+    IMkvReader* pReader,
+    long long start,
+    long long size_,
+    Entry* pEntry)
+{
+    if (size_ <= 0)
+        return false;
+
+    long long pos = start;
+    const long long stop = start + size_;
+
+    long len;
+
+    //parse the container for the level-1 element ID
+
+    const long long seekIdId = ReadUInt(pReader, pos, len);
+    //seekIdId;
+
+    if (seekIdId != 0x13AB)  //SeekID ID
+        return false;
+
+    if ((pos + len) > stop)
+        return false;
+
+    pos += len;  //consume SeekID id
+
+    const long long seekIdSize = ReadUInt(pReader, pos, len);
+
+    if (seekIdSize <= 0)
+        return false;
+
+    if ((pos + len) > stop)
+        return false;
+
+    pos += len;  //consume size of field
+
+    if ((pos + seekIdSize) > stop)
+        return false;
+
+    //Note that the SeekId payload really is serialized
+    //as a "Matroska integer", not as a plain binary value.
+    //In fact, Matroska requires that ID values in the
+    //stream exactly match the binary representation as listed
+    //in the Matroska specification.
+    //
+    //This parser is more liberal, and permits IDs to have
+    //any width.  (This could make the representation in the stream
+    //different from what's in the spec, but it doesn't matter here,
+    //since we always normalize "Matroska integer" values.)
+
+    pEntry->id = ReadUInt(pReader, pos, len);  //payload
+
+    if (pEntry->id <= 0)
+        return false;
+
+    if (len != seekIdSize)
+        return false;
+
+    pos += seekIdSize;  //consume SeekID payload
+
+    const long long seekPosId = ReadUInt(pReader, pos, len);
+
+    if (seekPosId != 0x13AC)  //SeekPos ID
+        return false;
+
+    if ((pos + len) > stop)
+        return false;
+
+    pos += len;  //consume id
+
+    const long long seekPosSize = ReadUInt(pReader, pos, len);
+
+    if (seekPosSize <= 0)
+        return false;
+
+    if ((pos + len) > stop)
+        return false;
+
+    pos += len;  //consume size
+
+    if ((pos + seekPosSize) > stop)
+        return false;
+
+    pEntry->pos = UnserializeUInt(pReader, pos, seekPosSize);
+
+    if (pEntry->pos < 0)
+        return false;
+
+    pos += seekPosSize;  //consume payload
+
+    if (pos != stop)
+        return false;
+
+    return true;
+}
+#endif
+
+
+Cues::Cues(
+    Segment* pSegment,
+    long long start_,
+    long long size_,
+    long long element_start,
+    long long element_size) :
+    m_pSegment(pSegment),
+    m_start(start_),
+    m_size(size_),
+    m_element_start(element_start),
+    m_element_size(element_size),
+    m_cue_points(NULL),
+    m_count(0),
+    m_preload_count(0),
+    m_pos(start_)
+{
+}
+
+
+Cues::~Cues()
+{
+    const long n = m_count + m_preload_count;
+
+    CuePoint** p = m_cue_points;
+    CuePoint** const q = p + n;
+
+    while (p != q)
+    {
+        CuePoint* const pCP = *p++;
+        assert(pCP);
+
+        delete pCP;
+    }
+
+    delete[] m_cue_points;
+}
+
+
+long Cues::GetCount() const
+{
+    if (m_cue_points == NULL)
+        return -1;
+
+    return m_count;  //TODO: really ignore preload count?
+}
+
+
+bool Cues::DoneParsing() const
+{
+    const long long stop = m_start + m_size;
+    return (m_pos >= stop);
+}
+
+
+void Cues::Init() const
+{
+    if (m_cue_points)
+        return;
+
+    assert(m_count == 0);
+    assert(m_preload_count == 0);
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    const long long stop = m_start + m_size;
+    long long pos = m_start;
+
+    long cue_points_size = 0;
+
+    while (pos < stop)
+    {
+        const long long idpos = pos;
+
+        long len;
+
+        const long long id = ReadUInt(pReader, pos, len);
+        assert(id >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, pos, len);
+        assert(size >= 0);
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume Size field
+        assert((pos + size) <= stop);
+
+        if (id == 0x3B)  //CuePoint ID
+            PreloadCuePoint(cue_points_size, idpos);
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+}
+
+
+void Cues::PreloadCuePoint(
+    long& cue_points_size,
+    long long pos) const
+{
+    assert(m_count == 0);
+
+    if (m_preload_count >= cue_points_size)
+    {
+        const long n = (cue_points_size <= 0) ? 2048 : 2*cue_points_size;
+
+        CuePoint** const qq = new CuePoint*[n];
+        CuePoint** q = qq;  //beginning of target
+
+        CuePoint** p = m_cue_points;                //beginning of source
+        CuePoint** const pp = p + m_preload_count;  //end of source
+
+        while (p != pp)
+            *q++ = *p++;
+
+        delete[] m_cue_points;
+
+        m_cue_points = qq;
+        cue_points_size = n;
+    }
+
+    CuePoint* const pCP = new CuePoint(m_preload_count, pos);
+    m_cue_points[m_preload_count++] = pCP;
+}
+
+
+bool Cues::LoadCuePoint() const
+{
+    //odbgstream os;
+    //os << "Cues::LoadCuePoint" << endl;
+
+    const long long stop = m_start + m_size;
+
+    if (m_pos >= stop)
+        return false;  //nothing else to do
+
+    Init();
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    while (m_pos < stop)
+    {
+        const long long idpos = m_pos;
+
+        long len;
+
+        const long long id = ReadUInt(pReader, m_pos, len);
+        assert(id >= 0);  //TODO
+        assert((m_pos + len) <= stop);
+
+        m_pos += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, m_pos, len);
+        assert(size >= 0);
+        assert((m_pos + len) <= stop);
+
+        m_pos += len;  //consume Size field
+        assert((m_pos + size) <= stop);
+
+        if (id != 0x3B)  //CuePoint ID
+        {
+            m_pos += size;  //consume payload
+            assert(m_pos <= stop);
+
+            continue;
+        }
+
+        assert(m_preload_count > 0);
+
+        CuePoint* const pCP = m_cue_points[m_count];
+        assert(pCP);
+        assert((pCP->GetTimeCode() >= 0) || (-pCP->GetTimeCode() == idpos));
+        if (pCP->GetTimeCode() < 0 && (-pCP->GetTimeCode() != idpos))
+            return false;
+
+        pCP->Load(pReader);
+        ++m_count;
+        --m_preload_count;
+
+        m_pos += size;  //consume payload
+        assert(m_pos <= stop);
+
+        return true;  //yes, we loaded a cue point
+    }
+
+    //return (m_pos < stop);
+    return false;  //no, we did not load a cue point
+}
+
+
+bool Cues::Find(
+    long long time_ns,
+    const Track* pTrack,
+    const CuePoint*& pCP,
+    const CuePoint::TrackPosition*& pTP) const
+{
+    assert(time_ns >= 0);
+    assert(pTrack);
+
+#if 0
+    LoadCuePoint();  //establish invariant
+
+    assert(m_cue_points);
+    assert(m_count > 0);
+
+    CuePoint** const ii = m_cue_points;
+    CuePoint** i = ii;
+
+    CuePoint** const jj = ii + m_count + m_preload_count;
+    CuePoint** j = jj;
+
+    pCP = *i;
+    assert(pCP);
+
+    if (time_ns <= pCP->GetTime(m_pSegment))
+    {
+        pTP = pCP->Find(pTrack);
+        return (pTP != NULL);
+    }
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[ii, i) <= time_ns
+        //[i, j)  ?
+        //[j, jj) > time_ns
+
+        CuePoint** const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        CuePoint* const pCP = *k;
+        assert(pCP);
+
+        pCP->Load(pReader);
+
+        const long long t = pCP->GetTime(m_pSegment);
+
+        if (t <= time_ns)
+            i = k + 1;
+        else
+            j = k;
+
+        assert(i <= j);
+    }
+
+    assert(i == j);
+    assert(i <= jj);
+    assert(i > ii);
+
+    pCP = *--i;
+    assert(pCP);
+    assert(pCP->GetTime(m_pSegment) <= time_ns);
+#else
+    if (m_cue_points == NULL)
+        return false;
+
+    if (m_count == 0)
+        return false;
+
+    CuePoint** const ii = m_cue_points;
+    CuePoint** i = ii;
+
+    CuePoint** const jj = ii + m_count;
+    CuePoint** j = jj;
+
+    pCP = *i;
+    assert(pCP);
+
+    if (time_ns <= pCP->GetTime(m_pSegment))
+    {
+        pTP = pCP->Find(pTrack);
+        return (pTP != NULL);
+    }
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[ii, i) <= time_ns
+        //[i, j)  ?
+        //[j, jj) > time_ns
+
+        CuePoint** const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        CuePoint* const pCP = *k;
+        assert(pCP);
+
+        const long long t = pCP->GetTime(m_pSegment);
+
+        if (t <= time_ns)
+            i = k + 1;
+        else
+            j = k;
+
+        assert(i <= j);
+    }
+
+    assert(i == j);
+    assert(i <= jj);
+    assert(i > ii);
+
+    pCP = *--i;
+    assert(pCP);
+    assert(pCP->GetTime(m_pSegment) <= time_ns);
+#endif
+
+    //TODO: here and elsewhere, it's probably not correct to search
+    //for the cue point with this time, and then search for a matching
+    //track.  In principle, the matching track could be on some earlier
+    //cue point, and with our current algorithm, we'd miss it.  To make
+    //this bullet-proof, we'd need to create a secondary structure,
+    //with a list of cue points that apply to a track, and then search
+    //that track-based structure for a matching cue point.
+
+    pTP = pCP->Find(pTrack);
+    return (pTP != NULL);
+}
+
+
+#if 0
+bool Cues::FindNext(
+    long long time_ns,
+    const Track* pTrack,
+    const CuePoint*& pCP,
+    const CuePoint::TrackPosition*& pTP) const
+{
+    pCP = 0;
+    pTP = 0;
+
+    if (m_count == 0)
+        return false;
+
+    assert(m_cue_points);
+
+    const CuePoint* const* const ii = m_cue_points;
+    const CuePoint* const* i = ii;
+
+    const CuePoint* const* const jj = ii + m_count;
+    const CuePoint* const* j = jj;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[ii, i) <= time_ns
+        //[i, j)  ?
+        //[j, jj) > time_ns
+
+        const CuePoint* const* const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        pCP = *k;
+        assert(pCP);
+
+        const long long t = pCP->GetTime(m_pSegment);
+
+        if (t <= time_ns)
+            i = k + 1;
+        else
+            j = k;
+
+        assert(i <= j);
+    }
+
+    assert(i == j);
+    assert(i <= jj);
+
+    if (i >= jj)  //time_ns is greater than max cue point
+        return false;
+
+    pCP = *i;
+    assert(pCP);
+    assert(pCP->GetTime(m_pSegment) > time_ns);
+
+    pTP = pCP->Find(pTrack);
+    return (pTP != NULL);
+}
+#endif
+
+
+const CuePoint* Cues::GetFirst() const
+{
+    if (m_cue_points == NULL)
+        return NULL;
+
+    if (m_count == 0)
+        return NULL;
+
+#if 0
+    LoadCuePoint();  //init cues
+
+    const size_t count = m_count + m_preload_count;
+
+    if (count == 0)  //weird
+        return NULL;
+#endif
+
+    CuePoint* const* const pp = m_cue_points;
+    assert(pp);
+
+    CuePoint* const pCP = pp[0];
+    assert(pCP);
+    assert(pCP->GetTimeCode() >= 0);
+
+    return pCP;
+}
+
+
+const CuePoint* Cues::GetLast() const
+{
+    if (m_cue_points == NULL)
+        return NULL;
+
+    if (m_count <= 0)
+        return NULL;
+
+#if 0
+    LoadCuePoint();  //init cues
+
+    const size_t count = m_count + m_preload_count;
+
+    if (count == 0)  //weird
+        return NULL;
+
+    const size_t index = count - 1;
+
+    CuePoint* const* const pp = m_cue_points;
+    assert(pp);
+
+    CuePoint* const pCP = pp[index];
+    assert(pCP);
+
+    pCP->Load(m_pSegment->m_pReader);
+    assert(pCP->GetTimeCode() >= 0);
+#else
+    const long index = m_count - 1;
+
+    CuePoint* const* const pp = m_cue_points;
+    assert(pp);
+
+    CuePoint* const pCP = pp[index];
+    assert(pCP);
+    assert(pCP->GetTimeCode() >= 0);
+#endif
+
+    return pCP;
+}
+
+
+const CuePoint* Cues::GetNext(const CuePoint* pCurr) const
+{
+    if (pCurr == NULL)
+        return NULL;
+
+    assert(pCurr->GetTimeCode() >= 0);
+    assert(m_cue_points);
+    assert(m_count >= 1);
+
+#if 0
+    const size_t count = m_count + m_preload_count;
+
+    size_t index = pCurr->m_index;
+    assert(index < count);
+
+    CuePoint* const* const pp = m_cue_points;
+    assert(pp);
+    assert(pp[index] == pCurr);
+
+    ++index;
+
+    if (index >= count)
+        return NULL;
+
+    CuePoint* const pNext = pp[index];
+    assert(pNext);
+
+    pNext->Load(m_pSegment->m_pReader);
+#else
+    long index = pCurr->m_index;
+    assert(index < m_count);
+
+    CuePoint* const* const pp = m_cue_points;
+    assert(pp);
+    assert(pp[index] == pCurr);
+
+    ++index;
+
+    if (index >= m_count)
+        return NULL;
+
+    CuePoint* const pNext = pp[index];
+    assert(pNext);
+    assert(pNext->GetTimeCode() >= 0);
+#endif
+
+    return pNext;
+}
+
+
+const BlockEntry* Cues::GetBlock(
+    const CuePoint* pCP,
+    const CuePoint::TrackPosition* pTP) const
+{
+    if (pCP == NULL)
+        return NULL;
+
+    if (pTP == NULL)
+        return NULL;
+
+    return m_pSegment->GetBlock(*pCP, *pTP);
+}
+
+
+const BlockEntry* Segment::GetBlock(
+    const CuePoint& cp,
+    const CuePoint::TrackPosition& tp)
+{
+    Cluster** const ii = m_clusters;
+    Cluster** i = ii;
+
+    const long count = m_clusterCount + m_clusterPreloadCount;
+
+    Cluster** const jj = ii + count;
+    Cluster** j = jj;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[ii, i) < pTP->m_pos
+        //[i, j) ?
+        //[j, jj)  > pTP->m_pos
+
+        Cluster** const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        Cluster* const pCluster = *k;
+        assert(pCluster);
+
+        //const long long pos_ = pCluster->m_pos;
+        //assert(pos_);
+        //const long long pos = pos_ * ((pos_ < 0) ? -1 : 1);
+
+        const long long pos = pCluster->GetPosition();
+        assert(pos >= 0);
+
+        if (pos < tp.m_pos)
+            i = k + 1;
+        else if (pos > tp.m_pos)
+            j = k;
+        else
+            return pCluster->GetEntry(cp, tp);
+    }
+
+    assert(i == j);
+    //assert(Cluster::HasBlockEntries(this, tp.m_pos));
+
+    Cluster* const pCluster = Cluster::Create(this, -1, tp.m_pos); //, -1);
+    assert(pCluster);
+
+    const ptrdiff_t idx = i - m_clusters;
+
+    PreloadCluster(pCluster, idx);
+    assert(m_clusters);
+    assert(m_clusterPreloadCount > 0);
+    assert(m_clusters[idx] == pCluster);
+
+    return pCluster->GetEntry(cp, tp);
+}
+
+
+const Cluster* Segment::FindOrPreloadCluster(long long requested_pos)
+{
+    if (requested_pos < 0)
+        return 0;
+
+    Cluster** const ii = m_clusters;
+    Cluster** i = ii;
+
+    const long count = m_clusterCount + m_clusterPreloadCount;
+
+    Cluster** const jj = ii + count;
+    Cluster** j = jj;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[ii, i) < pTP->m_pos
+        //[i, j) ?
+        //[j, jj)  > pTP->m_pos
+
+        Cluster** const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        Cluster* const pCluster = *k;
+        assert(pCluster);
+
+        //const long long pos_ = pCluster->m_pos;
+        //assert(pos_);
+        //const long long pos = pos_ * ((pos_ < 0) ? -1 : 1);
+
+        const long long pos = pCluster->GetPosition();
+        assert(pos >= 0);
+
+        if (pos < requested_pos)
+            i = k + 1;
+        else if (pos > requested_pos)
+            j = k;
+        else
+            return pCluster;
+    }
+
+    assert(i == j);
+    //assert(Cluster::HasBlockEntries(this, tp.m_pos));
+
+    Cluster* const pCluster = Cluster::Create(
+                                this,
+                                -1,
+                                requested_pos);
+                                //-1);
+    assert(pCluster);
+
+    const ptrdiff_t idx = i - m_clusters;
+
+    PreloadCluster(pCluster, idx);
+    assert(m_clusters);
+    assert(m_clusterPreloadCount > 0);
+    assert(m_clusters[idx] == pCluster);
+
+    return pCluster;
+}
+
+
+CuePoint::CuePoint(long idx, long long pos) :
+    m_element_start(0),
+    m_element_size(0),
+    m_index(idx),
+    m_timecode(-1 * pos),
+    m_track_positions(NULL),
+    m_track_positions_count(0)
+{
+    assert(pos > 0);
+}
+
+
+CuePoint::~CuePoint()
+{
+    delete[] m_track_positions;
+}
+
+
+void CuePoint::Load(IMkvReader* pReader)
+{
+    //odbgstream os;
+    //os << "CuePoint::Load(begin): timecode=" << m_timecode << endl;
+
+    if (m_timecode >= 0)  //already loaded
+        return;
+
+    assert(m_track_positions == NULL);
+    assert(m_track_positions_count == 0);
+
+    long long pos_ = -m_timecode;
+    const long long element_start = pos_;
+
+    long long stop;
+
+    {
+        long len;
+
+        const long long id = ReadUInt(pReader, pos_, len);
+        assert(id == 0x3B);  //CuePoint ID
+        if (id != 0x3B)
+            return;
+
+        pos_ += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, pos_, len);
+        assert(size >= 0);
+
+        pos_ += len;  //consume Size field
+        //pos_ now points to start of payload
+
+        stop = pos_ + size;
+    }
+
+    const long long element_size = stop - element_start;
+
+    long long pos = pos_;
+
+    //First count number of track positions
+
+    while (pos < stop)
+    {
+        long len;
+
+        const long long id = ReadUInt(pReader, pos, len);
+        assert(id >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, pos, len);
+        assert(size >= 0);
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume Size field
+        assert((pos + size) <= stop);
+
+        if (id == 0x33)  //CueTime ID
+            m_timecode = UnserializeUInt(pReader, pos, size);
+
+        else if (id == 0x37) //CueTrackPosition(s) ID
+            ++m_track_positions_count;
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(m_timecode >= 0);
+    assert(m_track_positions_count > 0);
+
+    //os << "CuePoint::Load(cont'd): idpos=" << idpos
+    //   << " timecode=" << m_timecode
+    //   << endl;
+
+    m_track_positions = new TrackPosition[m_track_positions_count];
+
+    //Now parse track positions
+
+    TrackPosition* p = m_track_positions;
+    pos = pos_;
+
+    while (pos < stop)
+    {
+        long len;
+
+        const long long id = ReadUInt(pReader, pos, len);
+        assert(id >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, pos, len);
+        assert(size >= 0);
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume Size field
+        assert((pos + size) <= stop);
+
+        if (id == 0x37) //CueTrackPosition(s) ID
+        {
+            TrackPosition& tp = *p++;
+            tp.Parse(pReader, pos, size);
+        }
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(size_t(p - m_track_positions) == m_track_positions_count);
+
+    m_element_start = element_start;
+    m_element_size = element_size;
+}
+
+
+
+void CuePoint::TrackPosition::Parse(
+    IMkvReader* pReader,
+    long long start_,
+    long long size_)
+{
+    const long long stop = start_ + size_;
+    long long pos = start_;
+
+    m_track = -1;
+    m_pos = -1;
+    m_block = 1;  //default
+
+    while (pos < stop)
+    {
+        long len;
+
+        const long long id = ReadUInt(pReader, pos, len);
+        assert(id >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, pos, len);
+        assert(size >= 0);
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume Size field
+        assert((pos + size) <= stop);
+
+        if (id == 0x77)  //CueTrack ID
+            m_track = UnserializeUInt(pReader, pos, size);
+
+        else if (id == 0x71)  //CueClusterPos ID
+            m_pos = UnserializeUInt(pReader, pos, size);
+
+        else if (id == 0x1378)  //CueBlockNumber
+            m_block = UnserializeUInt(pReader, pos, size);
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(m_pos >= 0);
+    assert(m_track > 0);
+    //assert(m_block > 0);
+}
+
+
+const CuePoint::TrackPosition* CuePoint::Find(const Track* pTrack) const
+{
+    assert(pTrack);
+
+    const long long n = pTrack->GetNumber();
+
+    const TrackPosition* i = m_track_positions;
+    const TrackPosition* const j = i + m_track_positions_count;
+
+    while (i != j)
+    {
+        const TrackPosition& p = *i++;
+
+        if (p.m_track == n)
+            return &p;
+    }
+
+    return NULL;  //no matching track number found
+}
+
+
+long long CuePoint::GetTimeCode() const
+{
+    return m_timecode;
+}
+
+long long CuePoint::GetTime(const Segment* pSegment) const
+{
+    assert(pSegment);
+    assert(m_timecode >= 0);
+
+    const SegmentInfo* const pInfo = pSegment->GetInfo();
+    assert(pInfo);
+
+    const long long scale = pInfo->GetTimeCodeScale();
+    assert(scale >= 1);
+
+    const long long time = scale * m_timecode;
+
+    return time;
+}
+
+
+#if 0
+long long Segment::Unparsed() const
+{
+    if (m_size < 0)
+        return LLONG_MAX;
+
+    const long long stop = m_start + m_size;
+
+    const long long result = stop - m_pos;
+    assert(result >= 0);
+
+    return result;
+}
+#else
+bool Segment::DoneParsing() const
+{
+    if (m_size < 0)
+    {
+        long long total, avail;
+
+        const int status = m_pReader->Length(&total, &avail);
+
+        if (status < 0)  //error
+            return true;  //must assume done
+
+        if (total < 0)
+            return false;  //assume live stream
+
+        return (m_pos >= total);
+    }
+
+    const long long stop = m_start + m_size;
+
+    return (m_pos >= stop);
+}
+#endif
+
+
+const Cluster* Segment::GetFirst() const
+{
+    if ((m_clusters == NULL) || (m_clusterCount <= 0))
+       return &m_eos;
+
+    Cluster* const pCluster = m_clusters[0];
+    assert(pCluster);
+
+    return pCluster;
+}
+
+
+const Cluster* Segment::GetLast() const
+{
+    if ((m_clusters == NULL) || (m_clusterCount <= 0))
+        return &m_eos;
+
+    const long idx = m_clusterCount - 1;
+
+    Cluster* const pCluster = m_clusters[idx];
+    assert(pCluster);
+
+    return pCluster;
+}
+
+
+unsigned long Segment::GetCount() const
+{
+    return m_clusterCount;
+}
+
+
+const Cluster* Segment::GetNext(const Cluster* pCurr)
+{
+    assert(pCurr);
+    assert(pCurr != &m_eos);
+    assert(m_clusters);
+
+    long idx =  pCurr->m_index;
+
+    if (idx >= 0)
+    {
+        assert(m_clusterCount > 0);
+        assert(idx < m_clusterCount);
+        assert(pCurr == m_clusters[idx]);
+
+        ++idx;
+
+        if (idx >= m_clusterCount)
+            return &m_eos;  //caller will LoadCluster as desired
+
+        Cluster* const pNext = m_clusters[idx];
+        assert(pNext);
+        assert(pNext->m_index >= 0);
+        assert(pNext->m_index == idx);
+
+        return pNext;
+    }
+
+    assert(m_clusterPreloadCount > 0);
+
+    long long pos = pCurr->m_element_start;
+
+    assert(m_size >= 0);  //TODO
+    const long long stop = m_start + m_size;  //end of segment
+
+    {
+        long len;
+
+        long long result = GetUIntLength(m_pReader, pos, len);
+        assert(result == 0);
+        assert((pos + len) <= stop);  //TODO
+        if (result != 0)
+            return NULL;
+
+        const long long id = ReadUInt(m_pReader, pos, len);
+        assert(id == 0x0F43B675);  //Cluster ID
+        if (id != 0x0F43B675)
+            return NULL;
+
+        pos += len;  //consume ID
+
+        //Read Size
+        result = GetUIntLength(m_pReader, pos, len);
+        assert(result == 0);  //TODO
+        assert((pos + len) <= stop);  //TODO
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+        assert(size > 0);  //TODO
+        //assert((pCurr->m_size <= 0) || (pCurr->m_size == size));
+
+        pos += len;  //consume length of size of element
+        assert((pos + size) <= stop);  //TODO
+
+        //Pos now points to start of payload
+
+        pos += size;  //consume payload
+    }
+
+    long long off_next = 0;
+
+    while (pos < stop)
+    {
+        long len;
+
+        long long result = GetUIntLength(m_pReader, pos, len);
+        assert(result == 0);
+        assert((pos + len) <= stop);  //TODO
+        if (result != 0)
+            return NULL;
+
+        const long long idpos = pos;  //pos of next (potential) cluster
+
+        const long long id = ReadUInt(m_pReader, idpos, len);
+        assert(id > 0);  //TODO
+
+        pos += len;  //consume ID
+
+        //Read Size
+        result = GetUIntLength(m_pReader, pos, len);
+        assert(result == 0);  //TODO
+        assert((pos + len) <= stop);  //TODO
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+        assert(size >= 0);  //TODO
+
+        pos += len;  //consume length of size of element
+        assert((pos + size) <= stop);  //TODO
+
+        //Pos now points to start of payload
+
+        if (size == 0)  //weird
+            continue;
+
+        if (id == 0x0F43B675)  //Cluster ID
+        {
+            const long long off_next_ = idpos - m_start;
+
+            long long pos_;
+            long len_;
+
+            const long status = Cluster::HasBlockEntries(
+                                    this,
+                                    off_next_,
+                                    pos_,
+                                    len_);
+
+            assert(status >= 0);
+
+            if (status > 0)
+            {
+                off_next = off_next_;
+                break;
+            }
+        }
+
+        pos += size;  //consume payload
+    }
+
+    if (off_next <= 0)
+        return 0;
+
+    Cluster** const ii = m_clusters + m_clusterCount;
+    Cluster** i = ii;
+
+    Cluster** const jj = ii + m_clusterPreloadCount;
+    Cluster** j = jj;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[0, i) < pos_next
+        //[i, j) ?
+        //[j, jj)  > pos_next
+
+        Cluster** const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        Cluster* const pNext = *k;
+        assert(pNext);
+        assert(pNext->m_index < 0);
+
+        //const long long pos_ = pNext->m_pos;
+        //assert(pos_);
+        //pos = pos_ * ((pos_ < 0) ? -1 : 1);
+
+        pos = pNext->GetPosition();
+
+        if (pos < off_next)
+            i = k + 1;
+        else if (pos > off_next)
+            j = k;
+        else
+            return pNext;
+    }
+
+    assert(i == j);
+
+    Cluster* const pNext = Cluster::Create(this,
+                                          -1,
+                                          off_next);
+    assert(pNext);
+
+    const ptrdiff_t idx_next = i - m_clusters;  //insertion position
+
+    PreloadCluster(pNext, idx_next);
+    assert(m_clusters);
+    assert(idx_next < m_clusterSize);
+    assert(m_clusters[idx_next] == pNext);
+
+    return pNext;
+}
+
+
+long Segment::ParseNext(
+    const Cluster* pCurr,
+    const Cluster*& pResult,
+    long long& pos,
+    long& len)
+{
+    assert(pCurr);
+    assert(!pCurr->EOS());
+    assert(m_clusters);
+
+    pResult = 0;
+
+    if (pCurr->m_index >= 0)  //loaded (not merely preloaded)
+    {
+        assert(m_clusters[pCurr->m_index] == pCurr);
+
+        const long next_idx = pCurr->m_index + 1;
+
+        if (next_idx < m_clusterCount)
+        {
+            pResult = m_clusters[next_idx];
+            return 0;  //success
+        }
+
+        //curr cluster is last among loaded
+
+        const long result = LoadCluster(pos, len);
+
+        if (result < 0)  //error or underflow
+            return result;
+
+        if (result > 0)  //no more clusters
+        {
+            //pResult = &m_eos;
+            return 1;
+        }
+
+        pResult = GetLast();
+        return 0;  //success
+    }
+
+    assert(m_pos > 0);
+
+    long long total, avail;
+
+    long status = m_pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
+
+    //interrogate curr cluster
+
+    pos = pCurr->m_element_start;
+
+    if (pCurr->m_element_size >= 0)
+        pos += pCurr->m_element_size;
+    else
+    {
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id = ReadUInt(m_pReader, pos, len);
+
+        if (id != 0x0F43B675)  //weird: not Cluster ID
+            return -1;
+
+        pos += len;  //consume ID
+
+        //Read Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+
+        if (size < 0) //error
+            return static_cast<long>(size);
+
+        pos += len;  //consume size field
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size == unknown_size)          //TODO: should never happen
+            return E_FILE_FORMAT_INVALID;  //TODO: resolve this
+
+        //assert((pCurr->m_size <= 0) || (pCurr->m_size == size));
+
+        if ((segment_stop >= 0) && ((pos + size) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        //Pos now points to start of payload
+
+        pos += size;  //consume payload (that is, the current cluster)
+        assert((segment_stop < 0) || (pos <= segment_stop));
+
+        //By consuming the payload, we are assuming that the curr
+        //cluster isn't interesting.  That is, we don't bother checking
+        //whether the payload of the curr cluster is less than what
+        //happens to be available (obtained via IMkvReader::Length).
+        //Presumably the caller has already dispensed with the current
+        //cluster, and really does want the next cluster.
+    }
+
+    //pos now points to just beyond the last fully-loaded cluster
+
+    for (;;)
+    {
+        const long status = DoParseNext(pResult, pos, len);
+
+        if (status <= 1)
+            return status;
+    }
+}
+
+
+long Segment::DoParseNext(
+    const Cluster*& pResult,
+    long long& pos,
+    long& len)
+{
+    long long total, avail;
+
+    long status = m_pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
+
+    //Parse next cluster.  This is strictly a parsing activity.
+    //Creation of a new cluster object happens later, after the
+    //parsing is done.
+
+    long long off_next = 0;
+    long long cluster_size = -1;
+
+    for (;;)
+    {
+        if ((total >= 0) && (pos >= total))
+            return 1;  //EOF
+
+        if ((segment_stop >= 0) && (pos >= segment_stop))
+            return 1;  //EOF
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long idpos = pos;             //absolute
+        const long long idoff = pos - m_start;   //relative
+
+        const long long id = ReadUInt(m_pReader, idpos, len);  //absolute
+
+        if (id < 0)  //error
+            return static_cast<long>(id);
+
+        if (id == 0)  //weird
+            return -1;  //generic error
+
+        pos += len;  //consume ID
+
+        //Read Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(m_pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(m_pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        pos += len;  //consume length of size of element
+
+        //Pos now points to start of payload
+
+        if (size == 0)  //weird
+            continue;
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if ((segment_stop >= 0) &&
+            (size != unknown_size) &&
+            ((pos + size) > segment_stop))
+        {
+            return E_FILE_FORMAT_INVALID;
+        }
+
+        if (id == 0x0C53BB6B)  //Cues ID
+        {
+            if (size == unknown_size)
+                return E_FILE_FORMAT_INVALID;
+
+            const long long element_stop = pos + size;
+
+            if ((segment_stop >= 0) && (element_stop > segment_stop))
+                return E_FILE_FORMAT_INVALID;
+
+            const long long element_start = idpos;
+            const long long element_size = element_stop - element_start;
+
+            if (m_pCues == NULL)
+            {
+                m_pCues = new Cues(this,
+                                    pos,
+                                    size,
+                                    element_start,
+                                    element_size);
+                assert(m_pCues);  //TODO
+            }
+
+            pos += size;  //consume payload
+            assert((segment_stop < 0) || (pos <= segment_stop));
+
+            continue;
+        }
+
+        if (id != 0x0F43B675)  //not a Cluster ID
+        {
+            if (size == unknown_size)
+                return E_FILE_FORMAT_INVALID;
+
+            pos += size;  //consume payload
+            assert((segment_stop < 0) || (pos <= segment_stop));
+
+            continue;
+        }
+
+#if 0 //this is commented-out to support incremental cluster parsing
+        len = static_cast<long>(size);
+
+        if (element_stop > avail)
+            return E_BUFFER_NOT_FULL;
+#endif
+
+        //We have a cluster.
+
+        off_next = idoff;
+
+        if (size != unknown_size)
+            cluster_size = size;
+
+        break;
+    }
+
+    assert(off_next > 0);  //have cluster
+
+    //We have parsed the next cluster.
+    //We have not created a cluster object yet.  What we need
+    //to do now is determine whether it has already be preloaded
+    //(in which case, an object for this cluster has already been
+    //created), and if not, create a new cluster object.
+
+    Cluster** const ii = m_clusters + m_clusterCount;
+    Cluster** i = ii;
+
+    Cluster** const jj = ii + m_clusterPreloadCount;
+    Cluster** j = jj;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[0, i) < pos_next
+        //[i, j) ?
+        //[j, jj)  > pos_next
+
+        Cluster** const k = i + (j - i) / 2;
+        assert(k < jj);
+
+        const Cluster* const pNext = *k;
+        assert(pNext);
+        assert(pNext->m_index < 0);
+
+        pos = pNext->GetPosition();
+        assert(pos >= 0);
+
+        if (pos < off_next)
+            i = k + 1;
+        else if (pos > off_next)
+            j = k;
+        else
+        {
+            pResult = pNext;
+            return 0;  //success
+        }
+    }
+
+    assert(i == j);
+
+    long long pos_;
+    long len_;
+
+    status = Cluster::HasBlockEntries(this, off_next, pos_, len_);
+
+    if (status < 0)  //error or underflow
+    {
+        pos = pos_;
+        len = len_;
+
+        return status;
+    }
+
+    if (status > 0)  //means "found at least one block entry"
+    {
+        Cluster* const pNext = Cluster::Create(this,
+                                                -1,   //preloaded
+                                                off_next);
+                                                //element_size);
+        assert(pNext);
+
+        const ptrdiff_t idx_next = i - m_clusters;  //insertion position
+
+        PreloadCluster(pNext, idx_next);
+        assert(m_clusters);
+        assert(idx_next < m_clusterSize);
+        assert(m_clusters[idx_next] == pNext);
+
+        pResult = pNext;
+        return 0;  //success
+    }
+
+    //status == 0 means "no block entries found"
+
+    if (cluster_size < 0)  //unknown size
+    {
+        const long long payload_pos = pos;  //absolute pos of cluster payload
+
+        for (;;)  //determine cluster size
+        {
+            if ((total >= 0) && (pos >= total))
+                break;
+
+            if ((segment_stop >= 0) && (pos >= segment_stop))
+                break;  //no more clusters
+
+            //Read ID
+
+            if ((pos + 1) > avail)
+            {
+                len = 1;
+                return E_BUFFER_NOT_FULL;
+            }
+
+            long long result = GetUIntLength(m_pReader, pos, len);
+
+            if (result < 0)  //error
+                return static_cast<long>(result);
+
+            if (result > 0)  //weird
+                return E_BUFFER_NOT_FULL;
+
+            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+                return E_FILE_FORMAT_INVALID;
+
+            if ((pos + len) > avail)
+                return E_BUFFER_NOT_FULL;
+
+            const long long idpos = pos;
+            const long long id = ReadUInt(m_pReader, idpos, len);
+
+            if (id < 0)  //error (or underflow)
+                return static_cast<long>(id);
+
+            //This is the distinguished set of ID's we use to determine
+            //that we have exhausted the sub-element's inside the cluster
+            //whose ID we parsed earlier.
+
+            if (id == 0x0F43B675)  //Cluster ID
+                break;
+
+            if (id == 0x0C53BB6B)  //Cues ID
+                break;
+
+            pos += len;  //consume ID (of sub-element)
+
+            //Read Size
+
+            if ((pos + 1) > avail)
+            {
+                len = 1;
+                return E_BUFFER_NOT_FULL;
+            }
+
+            result = GetUIntLength(m_pReader, pos, len);
+
+            if (result < 0)  //error
+                return static_cast<long>(result);
+
+            if (result > 0)  //weird
+                return E_BUFFER_NOT_FULL;
+
+            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+                return E_FILE_FORMAT_INVALID;
+
+            if ((pos + len) > avail)
+                return E_BUFFER_NOT_FULL;
+
+            const long long size = ReadUInt(m_pReader, pos, len);
+
+            if (size < 0)  //error
+                return static_cast<long>(size);
+
+            pos += len;  //consume size field of element
+
+            //pos now points to start of sub-element's payload
+
+            if (size == 0)  //weird
+                continue;
+
+            const long long unknown_size = (1LL << (7 * len)) - 1;
+
+            if (size == unknown_size)
+                return E_FILE_FORMAT_INVALID;  //not allowed for sub-elements
+
+            if ((segment_stop >= 0) && ((pos + size) > segment_stop))  //weird
+                return E_FILE_FORMAT_INVALID;
+
+            pos += size;  //consume payload of sub-element
+            assert((segment_stop < 0) || (pos <= segment_stop));
+        }  //determine cluster size
+
+        cluster_size = pos - payload_pos;
+        assert(cluster_size >= 0);  //TODO: handle cluster_size = 0
+
+        pos = payload_pos;  //reset and re-parse original cluster
+    }
+
+    pos += cluster_size;  //consume payload
+    assert((segment_stop < 0) || (pos <= segment_stop));
+
+    return 2;             //try to find a cluster that follows next
+}
+
+
+const Cluster* Segment::FindCluster(long long time_ns) const
+{
+    if ((m_clusters == NULL) || (m_clusterCount <= 0))
+        return &m_eos;
+
+    {
+        Cluster* const pCluster = m_clusters[0];
+        assert(pCluster);
+        assert(pCluster->m_index == 0);
+
+        if (time_ns <= pCluster->GetTime())
+            return pCluster;
+    }
+
+    //Binary search of cluster array
+
+    long i = 0;
+    long j = m_clusterCount;
+
+    while (i < j)
+    {
+        //INVARIANT:
+        //[0, i) <= time_ns
+        //[i, j) ?
+        //[j, m_clusterCount)  > time_ns
+
+        const long k = i + (j - i) / 2;
+        assert(k < m_clusterCount);
+
+        Cluster* const pCluster = m_clusters[k];
+        assert(pCluster);
+        assert(pCluster->m_index == k);
+
+        const long long t = pCluster->GetTime();
+
+        if (t <= time_ns)
+            i = k + 1;
+        else
+            j = k;
+
+        assert(i <= j);
+    }
+
+    assert(i == j);
+    assert(i > 0);
+    assert(i <= m_clusterCount);
+
+    const long k = i - 1;
+
+    Cluster* const pCluster = m_clusters[k];
+    assert(pCluster);
+    assert(pCluster->m_index == k);
+    assert(pCluster->GetTime() <= time_ns);
+
+    return pCluster;
+}
+
+
+#if 0
+const BlockEntry* Segment::Seek(
+    long long time_ns,
+    const Track* pTrack) const
+{
+    assert(pTrack);
+
+    if ((m_clusters == NULL) || (m_clusterCount <= 0))
+        return pTrack->GetEOS();
+
+    Cluster** const i = m_clusters;
+    assert(i);
+
+    {
+        Cluster* const pCluster = *i;
+        assert(pCluster);
+        assert(pCluster->m_index == 0);  //m_clusterCount > 0
+        assert(pCluster->m_pSegment == this);
+
+        if (time_ns <= pCluster->GetTime())
+            return pCluster->GetEntry(pTrack);
+    }
+
+    Cluster** const j = i + m_clusterCount;
+
+    if (pTrack->GetType() == 2)  //audio
+    {
+        //TODO: we could decide to use cues for this, as we do for video.
+        //But we only use it for video because looking around for a keyframe
+        //can get expensive.  Audio doesn't require anything special so a
+        //straight cluster search is good enough (we assume).
+
+        Cluster** lo = i;
+        Cluster** hi = j;
+
+        while (lo < hi)
+        {
+            //INVARIANT:
+            //[i, lo) <= time_ns
+            //[lo, hi) ?
+            //[hi, j)  > time_ns
+
+            Cluster** const mid = lo + (hi - lo) / 2;
+            assert(mid < hi);
+
+            Cluster* const pCluster = *mid;
+            assert(pCluster);
+            assert(pCluster->m_index == long(mid - m_clusters));
+            assert(pCluster->m_pSegment == this);
+
+            const long long t = pCluster->GetTime();
+
+            if (t <= time_ns)
+                lo = mid + 1;
+            else
+                hi = mid;
+
+            assert(lo <= hi);
+        }
+
+        assert(lo == hi);
+        assert(lo > i);
+        assert(lo <= j);
+
+        while (lo > i)
+        {
+            Cluster* const pCluster = *--lo;
+            assert(pCluster);
+            assert(pCluster->GetTime() <= time_ns);
+
+            const BlockEntry* const pBE = pCluster->GetEntry(pTrack);
+
+            if ((pBE != 0) && !pBE->EOS())
+                return pBE;
+
+            //landed on empty cluster (no entries)
+        }
+
+        return pTrack->GetEOS();  //weird
+    }
+
+    assert(pTrack->GetType() == 1);  //video
+
+    Cluster** lo = i;
+    Cluster** hi = j;
+
+    while (lo < hi)
+    {
+        //INVARIANT:
+        //[i, lo) <= time_ns
+        //[lo, hi) ?
+        //[hi, j)  > time_ns
+
+        Cluster** const mid = lo + (hi - lo) / 2;
+        assert(mid < hi);
+
+        Cluster* const pCluster = *mid;
+        assert(pCluster);
+
+        const long long t = pCluster->GetTime();
+
+        if (t <= time_ns)
+            lo = mid + 1;
+        else
+            hi = mid;
+
+        assert(lo <= hi);
+    }
+
+    assert(lo == hi);
+    assert(lo > i);
+    assert(lo <= j);
+
+    Cluster* pCluster = *--lo;
+    assert(pCluster);
+    assert(pCluster->GetTime() <= time_ns);
+
+    {
+        const BlockEntry* const pBE = pCluster->GetEntry(pTrack, time_ns);
+
+        if ((pBE != 0) && !pBE->EOS())  //found a keyframe
+            return pBE;
+    }
+
+    const VideoTrack* const pVideo = static_cast<const VideoTrack*>(pTrack);
+
+    while (lo != i)
+    {
+        pCluster = *--lo;
+        assert(pCluster);
+        assert(pCluster->GetTime() <= time_ns);
+
+        const BlockEntry* const pBlockEntry = pCluster->GetMaxKey(pVideo);
+
+        if ((pBlockEntry != 0) && !pBlockEntry->EOS())
+            return pBlockEntry;
+    }
+
+    //weird: we're on the first cluster, but no keyframe found
+    //should never happen but we must return something anyway
+
+    return pTrack->GetEOS();
+}
+#endif
+
+
+#if 0
+bool Segment::SearchCues(
+    long long time_ns,
+    Track* pTrack,
+    Cluster*& pCluster,
+    const BlockEntry*& pBlockEntry,
+    const CuePoint*& pCP,
+    const CuePoint::TrackPosition*& pTP)
+{
+    if (pTrack->GetType() != 1)  //not video
+        return false;  //TODO: for now, just handle video stream
+
+    if (m_pCues == NULL)
+        return false;
+
+    if (!m_pCues->Find(time_ns, pTrack, pCP, pTP))
+        return false;  //weird
+
+    assert(pCP);
+    assert(pTP);
+    assert(pTP->m_track == pTrack->GetNumber());
+
+    //We have the cue point and track position we want,
+    //so we now need to search for the cluster having
+    //the indicated position.
+
+    return GetCluster(pCP, pTP, pCluster, pBlockEntry);
+}
+#endif
+
+
+const Tracks* Segment::GetTracks() const
+{
+    return m_pTracks;
+}
+
+
+const SegmentInfo* Segment::GetInfo() const
+{
+    return m_pInfo;
+}
+
+
+const Cues* Segment::GetCues() const
+{
+    return m_pCues;
+}
+
+
+const Chapters* Segment::GetChapters() const
+{
+  return m_pChapters;
+}
+
+
+const SeekHead* Segment::GetSeekHead() const
+{
+    return m_pSeekHead;
+}
+
+
+long long Segment::GetDuration() const
+{
+    assert(m_pInfo);
+    return m_pInfo->GetDuration();
+}
+
+
+Chapters::Chapters(
+    Segment* pSegment,
+    long long payload_start,
+    long long payload_size,
+    long long element_start,
+    long long element_size) :
+    m_pSegment(pSegment),
+    m_start(payload_start),
+    m_size(payload_size),
+    m_element_start(element_start),
+    m_element_size(element_size),
+    m_editions(NULL),
+    m_editions_size(0),
+    m_editions_count(0)
+{
+}
+
+
+Chapters::~Chapters()
+{
+    while (m_editions_count > 0)
+    {
+        Edition& e = m_editions[--m_editions_count];
+        e.Clear();
+    }
+}
+
+
+long Chapters::Parse()
+{
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long pos = m_start;  // payload start
+    const long long stop = pos + m_size;  // payload stop
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        long status = ParseElementHeader(
+                        pReader,
+                        pos,
+                        stop,
+                        id,
+                        size);
+
+        if (status < 0)  // error
+            return status;
+
+        if (size == 0)  // weird
+            continue;
+
+        if (id == 0x05B9)  // EditionEntry ID
+        {
+            status = ParseEdition(pos, size);
+
+            if (status < 0)  // error
+                return status;
+        }
+
+        pos += size;
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+    return 0;
+}
+
+
+int Chapters::GetEditionCount() const
+{
+    return m_editions_count;
+}
+
+
+const Chapters::Edition* Chapters::GetEdition(int idx) const
+{
+    if (idx < 0)
+        return NULL;
+
+    if (idx >= m_editions_count)
+        return NULL;
+
+    return m_editions + idx;
+}
+
+
+bool Chapters::ExpandEditionsArray()
+{
+    if (m_editions_size > m_editions_count)
+        return true;  // nothing else to do
+
+    const int size = (m_editions_size == 0) ? 1 : 2 * m_editions_size;
+
+    Edition* const editions = new (std::nothrow) Edition[size];
+
+    if (editions == NULL)
+        return false;
+
+    for (int idx = 0; idx < m_editions_count; ++idx)
+    {
+        m_editions[idx].ShallowCopy(editions[idx]);
+    }
+
+    delete[] m_editions;
+    m_editions = editions;
+
+    m_editions_size = size;
+    return true;
+}
+
+
+long Chapters::ParseEdition(
+    long long pos,
+    long long size)
+{
+    if (!ExpandEditionsArray())
+        return -1;
+
+    Edition& e = m_editions[m_editions_count++];
+    e.Init();
+
+    return e.Parse(m_pSegment->m_pReader, pos, size);
+}
+
+
+Chapters::Edition::Edition()
+{
+}
+
+
+Chapters::Edition::~Edition()
+{
+}
+
+
+int Chapters::Edition::GetAtomCount() const
+{
+    return m_atoms_count;
+}
+
+
+const Chapters::Atom* Chapters::Edition::GetAtom(int index) const
+{
+    if (index < 0)
+        return NULL;
+
+    if (index >= m_atoms_count)
+        return NULL;
+
+    return m_atoms + index;
+}
+
+
+void Chapters::Edition::Init()
+{
+    m_atoms = NULL;
+    m_atoms_size = 0;
+    m_atoms_count = 0;
+}
+
+
+void Chapters::Edition::ShallowCopy(Edition& rhs) const
+{
+    rhs.m_atoms = m_atoms;
+    rhs.m_atoms_size = m_atoms_size;
+    rhs.m_atoms_count = m_atoms_count;
+}
+
+
+void Chapters::Edition::Clear()
+{
+    while (m_atoms_count > 0)
+    {
+        Atom& a = m_atoms[--m_atoms_count];
+        a.Clear();
+    }
+
+    delete[] m_atoms;
+    m_atoms = NULL;
+
+    m_atoms_size = 0;
+}
+
+
+long Chapters::Edition::Parse(
+    IMkvReader* pReader,
+    long long pos,
+    long long size)
+{
+    const long long stop = pos + size;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        long status = ParseElementHeader(
+                        pReader,
+                        pos,
+                        stop,
+                        id,
+                        size);
+
+        if (status < 0)  // error
+            return status;
+
+        if (size == 0)  // weird
+            continue;
+
+        if (id == 0x36)  // Atom ID
+        {
+            status = ParseAtom(pReader, pos, size);
+
+            if (status < 0)  // error
+                return status;
+        }
+
+        pos += size;
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+    return 0;
+}
+
+
+long Chapters::Edition::ParseAtom(
+    IMkvReader* pReader,
+    long long pos,
+    long long size)
+{
+    if (!ExpandAtomsArray())
+        return -1;
+
+    Atom& a = m_atoms[m_atoms_count++];
+    a.Init();
+
+    return a.Parse(pReader, pos, size);
+}
+
+
+bool Chapters::Edition::ExpandAtomsArray()
+{
+    if (m_atoms_size > m_atoms_count)
+        return true;  // nothing else to do
+
+    const int size = (m_atoms_size == 0) ? 1 : 2 * m_atoms_size;
+
+    Atom* const atoms = new (std::nothrow) Atom[size];
+
+    if (atoms == NULL)
+        return false;
+
+    for (int idx = 0; idx < m_atoms_count; ++idx)
+    {
+        m_atoms[idx].ShallowCopy(atoms[idx]);
+    }
+
+    delete[] m_atoms;
+    m_atoms = atoms;
+
+    m_atoms_size = size;
+    return true;
+}
+
+
+Chapters::Atom::Atom()
+{
+}
+
+
+Chapters::Atom::~Atom()
+{
+}
+
+
+unsigned long long Chapters::Atom::GetUID() const
+{
+    return m_uid;
+}
+
+
+const char* Chapters::Atom::GetStringUID() const
+{
+    return m_string_uid;
+}
+
+
+long long Chapters::Atom::GetStartTimecode() const
+{
+    return m_start_timecode;
+}
+
+
+long long Chapters::Atom::GetStopTimecode() const
+{
+    return m_stop_timecode;
+}
+
+
+long long Chapters::Atom::GetStartTime(const Chapters* pChapters) const
+{
+    return GetTime(pChapters, m_start_timecode);
+}
+
+
+long long Chapters::Atom::GetStopTime(const Chapters* pChapters) const
+{
+    return GetTime(pChapters, m_stop_timecode);
+}
+
+
+int Chapters::Atom::GetDisplayCount() const
+{
+    return m_displays_count;
+}
+
+
+const Chapters::Display* Chapters::Atom::GetDisplay(int index) const
+{
+    if (index < 0)
+        return NULL;
+
+    if (index >= m_displays_count)
+        return NULL;
+
+    return m_displays + index;
+}
+
+
+void Chapters::Atom::Init()
+{
+    m_string_uid = NULL;
+    m_uid = 0;
+    m_start_timecode = -1;
+    m_stop_timecode = -1;
+
+    m_displays = NULL;
+    m_displays_size = 0;
+    m_displays_count = 0;
+}
+
+
+void Chapters::Atom::ShallowCopy(Atom& rhs) const
+{
+    rhs.m_string_uid = m_string_uid;
+    rhs.m_uid = m_uid;
+    rhs.m_start_timecode = m_start_timecode;
+    rhs.m_stop_timecode = m_stop_timecode;
+
+    rhs.m_displays = m_displays;
+    rhs.m_displays_size = m_displays_size;
+    rhs.m_displays_count = m_displays_count;
+}
+
+
+void Chapters::Atom::Clear()
+{
+    delete[] m_string_uid;
+    m_string_uid = NULL;
+
+    while (m_displays_count > 0)
+    {
+        Display& d = m_displays[--m_displays_count];
+        d.Clear();
+    }
+
+    delete[] m_displays;
+    m_displays = NULL;
+
+    m_displays_size = 0;
+}
+
+
+long Chapters::Atom::Parse(
+    IMkvReader* pReader,
+    long long pos,
+    long long size)
+{
+    const long long stop = pos + size;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        long status = ParseElementHeader(
+                        pReader,
+                        pos,
+                        stop,
+                        id,
+                        size);
+
+        if (status < 0)  // error
+            return status;
+
+        if (size == 0)  // weird
+            continue;
+
+        if (id == 0x00)  // Display ID
+        {
+            status = ParseDisplay(pReader, pos, size);
+
+            if (status < 0)  // error
+                return status;
+        }
+        else if (id == 0x1654)  // StringUID ID
+        {
+            status = UnserializeString(pReader, pos, size, m_string_uid);
+
+            if (status < 0)  // error
+                return status;
+        }
+        else if (id == 0x33C4)  // UID ID
+        {
+            const long long val = UnserializeUInt(pReader, pos, size);
+
+            if (val < 0)  // error
+                return static_cast<long>(val);
+
+            m_uid = val;
+        }
+        else if (id == 0x11)  // TimeStart ID
+        {
+            const long long val = UnserializeUInt(pReader, pos, size);
+
+            if (val < 0)  // error
+                return static_cast<long>(val);
+
+            m_start_timecode = val;
+        }
+        else if (id == 0x12)  // TimeEnd ID
+        {
+            const long long val = UnserializeUInt(pReader, pos, size);
+
+            if (val < 0)  // error
+                return static_cast<long>(val);
+
+            m_stop_timecode = val;
+        }
+
+        pos += size;
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+    return 0;
+}
+
+
+long long Chapters::Atom::GetTime(
+    const Chapters* pChapters,
+    long long timecode)
+{
+    if (pChapters == NULL)
+        return -1;
+
+    Segment* const pSegment = pChapters->m_pSegment;
+
+    if (pSegment == NULL)  // weird
+        return -1;
+
+    const SegmentInfo* const pInfo = pSegment->GetInfo();
+
+    if (pInfo == NULL)
+        return -1;
+
+    const long long timecode_scale = pInfo->GetTimeCodeScale();
+
+    if (timecode_scale < 1)  // weird
+        return -1;
+
+    if (timecode < 0)
+        return -1;
+
+    const long long result = timecode_scale * timecode;
+
+    return result;
+}
+
+
+long Chapters::Atom::ParseDisplay(
+    IMkvReader* pReader,
+    long long pos,
+    long long size)
+{
+    if (!ExpandDisplaysArray())
+        return -1;
+
+    Display& d = m_displays[m_displays_count++];
+    d.Init();
+
+    return d.Parse(pReader, pos, size);
+}
+
+
+bool Chapters::Atom::ExpandDisplaysArray()
+{
+    if (m_displays_size > m_displays_count)
+        return true;  // nothing else to do
+
+    const int size = (m_displays_size == 0) ? 1 : 2 * m_displays_size;
+
+    Display* const displays = new (std::nothrow) Display[size];
+
+    if (displays == NULL)
+        return false;
+
+    for (int idx = 0; idx < m_displays_count; ++idx)
+    {
+        m_displays[idx].ShallowCopy(displays[idx]);
+    }
+
+    delete[] m_displays;
+    m_displays = displays;
+
+    m_displays_size = size;
+    return true;
+}
+
+
+Chapters::Display::Display()
+{
+}
+
+
+Chapters::Display::~Display()
+{
+}
+
+
+const char* Chapters::Display::GetString() const
+{
+    return m_string;
+}
+
+
+const char* Chapters::Display::GetLanguage() const
+{
+    return m_language;
+}
+
+
+const char* Chapters::Display::GetCountry() const
+{
+    return m_country;
+}
+
+
+void Chapters::Display::Init()
+{
+    m_string = NULL;
+    m_language = NULL;
+    m_country = NULL;
+}
+
+
+void Chapters::Display::ShallowCopy(Display& rhs) const
+{
+    rhs.m_string = m_string;
+    rhs.m_language = m_language;
+    rhs.m_country = m_country;
+}
+
+
+void Chapters::Display::Clear()
+{
+    delete[] m_string;
+    m_string = NULL;
+
+    delete[] m_language;
+    m_language = NULL;
+
+    delete[] m_country;
+    m_country = NULL;
+}
+
+
+long Chapters::Display::Parse(
+    IMkvReader* pReader,
+    long long pos,
+    long long size)
+{
+    const long long stop = pos + size;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        long status = ParseElementHeader(
+                        pReader,
+                        pos,
+                        stop,
+                        id,
+                        size);
+
+        if (status < 0)  // error
+            return status;
+
+        if (size == 0)  // weird
+            continue;
+
+        if (id == 0x05)  // ChapterString ID
+        {
+            status = UnserializeString(pReader, pos, size, m_string);
+
+            if (status)
+              return status;
+        }
+        else if (id == 0x037C)  // ChapterLanguage ID
+        {
+            status = UnserializeString(pReader, pos, size, m_language);
+
+            if (status)
+              return status;
+        }
+        else if (id == 0x037E)  // ChapterCountry ID
+        {
+            status = UnserializeString(pReader, pos, size, m_country);
+
+            if (status)
+              return status;
+        }
+
+        pos += size;
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+    return 0;
+}
+
+
+SegmentInfo::SegmentInfo(
+    Segment* pSegment,
+    long long start,
+    long long size_,
+    long long element_start,
+    long long element_size) :
+    m_pSegment(pSegment),
+    m_start(start),
+    m_size(size_),
+    m_element_start(element_start),
+    m_element_size(element_size),
+    m_pMuxingAppAsUTF8(NULL),
+    m_pWritingAppAsUTF8(NULL),
+    m_pTitleAsUTF8(NULL)
+{
+}
+
+SegmentInfo::~SegmentInfo()
+{
+    delete[] m_pMuxingAppAsUTF8;
+    m_pMuxingAppAsUTF8 = NULL;
+
+    delete[] m_pWritingAppAsUTF8;
+    m_pWritingAppAsUTF8 = NULL;
+
+    delete[] m_pTitleAsUTF8;
+    m_pTitleAsUTF8 = NULL;
+}
+
+
+long SegmentInfo::Parse()
+{
+    assert(m_pMuxingAppAsUTF8 == NULL);
+    assert(m_pWritingAppAsUTF8 == NULL);
+    assert(m_pTitleAsUTF8 == NULL);
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long pos = m_start;
+    const long long stop = m_start + m_size;
+
+    m_timecodeScale = 1000000;
+    m_duration = -1;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (id == 0x0AD7B1)  //Timecode Scale
+        {
+            m_timecodeScale = UnserializeUInt(pReader, pos, size);
+
+            if (m_timecodeScale <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x0489)  //Segment duration
+        {
+            const long status = UnserializeFloat(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    m_duration);
+
+            if (status < 0)
+                return status;
+
+            if (m_duration < 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x0D80)  //MuxingApp
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    m_pMuxingAppAsUTF8);
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x1741)  //WritingApp
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    m_pWritingAppAsUTF8);
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x3BA9)  //Title
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    m_pTitleAsUTF8);
+
+            if (status)
+                return status;
+        }
+
+        pos += size;
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    return 0;
+}
+
+
+long long SegmentInfo::GetTimeCodeScale() const
+{
+    return m_timecodeScale;
+}
+
+
+long long SegmentInfo::GetDuration() const
+{
+    if (m_duration < 0)
+        return -1;
+
+    assert(m_timecodeScale >= 1);
+
+    const double dd = double(m_duration) * double(m_timecodeScale);
+    const long long d = static_cast<long long>(dd);
+
+    return d;
+}
+
+const char* SegmentInfo::GetMuxingAppAsUTF8() const
+{
+    return m_pMuxingAppAsUTF8;
+}
+
+
+const char* SegmentInfo::GetWritingAppAsUTF8() const
+{
+    return m_pWritingAppAsUTF8;
+}
+
+const char* SegmentInfo::GetTitleAsUTF8() const
+{
+    return m_pTitleAsUTF8;
+}
+
+///////////////////////////////////////////////////////////////
+// ContentEncoding element
+ContentEncoding::ContentCompression::ContentCompression()
+    : algo(0),
+      settings(NULL),
+      settings_len(0) {
+}
+
+ContentEncoding::ContentCompression::~ContentCompression() {
+  delete [] settings;
+}
+
+ContentEncoding::ContentEncryption::ContentEncryption()
+    : algo(0),
+      key_id(NULL),
+      key_id_len(0),
+      signature(NULL),
+      signature_len(0),
+      sig_key_id(NULL),
+      sig_key_id_len(0),
+      sig_algo(0),
+      sig_hash_algo(0) {
+}
+
+ContentEncoding::ContentEncryption::~ContentEncryption() {
+  delete [] key_id;
+  delete [] signature;
+  delete [] sig_key_id;
+}
+
+ContentEncoding::ContentEncoding()
+    : compression_entries_(NULL),
+      compression_entries_end_(NULL),
+      encryption_entries_(NULL),
+      encryption_entries_end_(NULL),
+      encoding_order_(0),
+      encoding_scope_(1),
+      encoding_type_(0) {
+}
+
+ContentEncoding::~ContentEncoding() {
+  ContentCompression** comp_i = compression_entries_;
+  ContentCompression** const comp_j = compression_entries_end_;
+
+  while (comp_i != comp_j) {
+    ContentCompression* const comp = *comp_i++;
+    delete comp;
+  }
+
+  delete [] compression_entries_;
+
+  ContentEncryption** enc_i = encryption_entries_;
+  ContentEncryption** const enc_j = encryption_entries_end_;
+
+  while (enc_i != enc_j) {
+    ContentEncryption* const enc = *enc_i++;
+    delete enc;
+  }
+
+  delete [] encryption_entries_;
+}
+
+
+const ContentEncoding::ContentCompression*
+ContentEncoding::GetCompressionByIndex(unsigned long idx) const {
+  const ptrdiff_t count = compression_entries_end_ - compression_entries_;
+  assert(count >= 0);
+
+  if (idx >= static_cast<unsigned long>(count))
+    return NULL;
+
+  return compression_entries_[idx];
+}
+
+unsigned long ContentEncoding::GetCompressionCount() const {
+  const ptrdiff_t count = compression_entries_end_ - compression_entries_;
+  assert(count >= 0);
+
+  return static_cast<unsigned long>(count);
+}
+
+const ContentEncoding::ContentEncryption*
+ContentEncoding::GetEncryptionByIndex(unsigned long idx) const {
+  const ptrdiff_t count = encryption_entries_end_ - encryption_entries_;
+  assert(count >= 0);
+
+  if (idx >= static_cast<unsigned long>(count))
+    return NULL;
+
+  return encryption_entries_[idx];
+}
+
+unsigned long ContentEncoding::GetEncryptionCount() const {
+  const ptrdiff_t count = encryption_entries_end_ - encryption_entries_;
+  assert(count >= 0);
+
+  return static_cast<unsigned long>(count);
+}
+
+long ContentEncoding::ParseContentEncAESSettingsEntry(
+    long long start,
+    long long size,
+    IMkvReader* pReader,
+    ContentEncAESSettings* aes) {
+  assert(pReader);
+  assert(aes);
+
+  long long pos = start;
+  const long long stop = start + size;
+
+  while (pos < stop) {
+    long long id, size;
+    const long status = ParseElementHeader(pReader,
+                                           pos,
+                                           stop,
+                                           id,
+                                           size);
+    if (status < 0)  //error
+      return status;
+
+    if (id == 0x7E8) {
+      // AESSettingsCipherMode
+      aes->cipher_mode = UnserializeUInt(pReader, pos, size);
+      if (aes->cipher_mode != 1)
+        return E_FILE_FORMAT_INVALID;
+    }
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  return 0;
+}
+
+long ContentEncoding::ParseContentEncodingEntry(long long start,
+                                                long long size,
+                                                IMkvReader* pReader) {
+  assert(pReader);
+
+  long long pos = start;
+  const long long stop = start + size;
+
+  // Count ContentCompression and ContentEncryption elements.
+  int compression_count = 0;
+  int encryption_count = 0;
+
+  while (pos < stop) {
+    long long id, size;
+    const long status = ParseElementHeader(pReader,
+                                           pos,
+                                           stop,
+                                           id,
+                                           size);
+    if (status < 0)  //error
+      return status;
+
+    if (id == 0x1034)  // ContentCompression ID
+      ++compression_count;
+
+    if (id == 0x1035)  // ContentEncryption ID
+      ++encryption_count;
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  if (compression_count <= 0 && encryption_count <= 0)
+    return -1;
+
+  if (compression_count > 0) {
+    compression_entries_ =
+        new (std::nothrow) ContentCompression*[compression_count];
+    if (!compression_entries_)
+      return -1;
+    compression_entries_end_ = compression_entries_;
+  }
+
+  if (encryption_count > 0) {
+    encryption_entries_ =
+        new (std::nothrow) ContentEncryption*[encryption_count];
+    if (!encryption_entries_) {
+      delete [] compression_entries_;
+      return -1;
+    }
+    encryption_entries_end_ = encryption_entries_;
+  }
+
+  pos = start;
+  while (pos < stop) {
+    long long id, size;
+    long status = ParseElementHeader(pReader,
+                                     pos,
+                                     stop,
+                                     id,
+                                     size);
+    if (status < 0)  //error
+      return status;
+
+    if (id == 0x1031) {
+      // ContentEncodingOrder
+      encoding_order_ = UnserializeUInt(pReader, pos, size);
+    } else if (id == 0x1032) {
+      // ContentEncodingScope
+      encoding_scope_ = UnserializeUInt(pReader, pos, size);
+      if (encoding_scope_ < 1)
+        return -1;
+    } else if (id == 0x1033) {
+      // ContentEncodingType
+      encoding_type_ = UnserializeUInt(pReader, pos, size);
+    } else if (id == 0x1034) {
+      // ContentCompression ID
+      ContentCompression* const compression =
+        new (std::nothrow) ContentCompression();
+      if (!compression)
+        return -1;
+
+      status = ParseCompressionEntry(pos, size, pReader, compression);
+      if (status) {
+        delete compression;
+        return status;
+      }
+      *compression_entries_end_++ = compression;
+    } else if (id == 0x1035) {
+      // ContentEncryption ID
+      ContentEncryption* const encryption =
+          new (std::nothrow) ContentEncryption();
+      if (!encryption)
+        return -1;
+
+      status = ParseEncryptionEntry(pos, size, pReader, encryption);
+      if (status) {
+        delete encryption;
+        return status;
+      }
+      *encryption_entries_end_++ = encryption;
+    }
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  assert(pos == stop);
+  return 0;
+}
+
+long ContentEncoding::ParseCompressionEntry(
+    long long start,
+    long long size,
+    IMkvReader* pReader,
+    ContentCompression* compression) {
+  assert(pReader);
+  assert(compression);
+
+  long long pos = start;
+  const long long stop = start + size;
+
+  bool valid = false;
+
+  while (pos < stop) {
+    long long id, size;
+    const long status = ParseElementHeader(pReader,
+                                           pos,
+                                           stop,
+                                           id,
+                                           size);
+    if (status < 0)  //error
+      return status;
+
+    if (id == 0x254) {
+      // ContentCompAlgo
+      long long algo = UnserializeUInt(pReader, pos, size);
+      if (algo < 0)
+        return E_FILE_FORMAT_INVALID;
+      compression->algo = algo;
+      valid = true;
+    } else if (id == 0x255) {
+      // ContentCompSettings
+      if (size <= 0)
+        return E_FILE_FORMAT_INVALID;
+
+      const size_t buflen = static_cast<size_t>(size);
+      typedef unsigned char* buf_t;
+      const buf_t buf = new (std::nothrow) unsigned char[buflen];
+      if (buf == NULL)
+        return -1;
+
+      const int read_status = pReader->Read(pos, buflen, buf);
+      if (read_status) {
+        delete [] buf;
+        return status;
+      }
+
+      compression->settings = buf;
+      compression->settings_len = buflen;
+    }
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  // ContentCompAlgo is mandatory
+  if (!valid)
+    return E_FILE_FORMAT_INVALID;
+
+  return 0;
+}
+
+long ContentEncoding::ParseEncryptionEntry(
+    long long start,
+    long long size,
+    IMkvReader* pReader,
+    ContentEncryption* encryption) {
+  assert(pReader);
+  assert(encryption);
+
+  long long pos = start;
+  const long long stop = start + size;
+
+  while (pos < stop) {
+    long long id, size;
+    const long status = ParseElementHeader(pReader,
+                                           pos,
+                                           stop,
+                                           id,
+                                           size);
+    if (status < 0)  //error
+      return status;
+
+    if (id == 0x7E1) {
+      // ContentEncAlgo
+      encryption->algo = UnserializeUInt(pReader, pos, size);
+      if (encryption->algo != 5)
+        return E_FILE_FORMAT_INVALID;
+    } else if (id == 0x7E2) {
+      // ContentEncKeyID
+      delete[] encryption->key_id;
+      encryption->key_id = NULL;
+      encryption->key_id_len = 0;
+
+      if (size <= 0)
+        return E_FILE_FORMAT_INVALID;
+
+      const size_t buflen = static_cast<size_t>(size);
+      typedef unsigned char* buf_t;
+      const buf_t buf = new (std::nothrow) unsigned char[buflen];
+      if (buf == NULL)
+        return -1;
+
+      const int read_status = pReader->Read(pos, buflen, buf);
+      if (read_status) {
+        delete [] buf;
+        return status;
+      }
+
+      encryption->key_id = buf;
+      encryption->key_id_len = buflen;
+    } else if (id == 0x7E3) {
+      // ContentSignature
+      delete[] encryption->signature;
+      encryption->signature = NULL;
+      encryption->signature_len = 0;
+
+      if (size <= 0)
+        return E_FILE_FORMAT_INVALID;
+
+      const size_t buflen = static_cast<size_t>(size);
+      typedef unsigned char* buf_t;
+      const buf_t buf = new (std::nothrow) unsigned char[buflen];
+      if (buf == NULL)
+        return -1;
+
+      const int read_status = pReader->Read(pos, buflen, buf);
+      if (read_status) {
+        delete [] buf;
+        return status;
+      }
+
+      encryption->signature = buf;
+      encryption->signature_len = buflen;
+    } else if (id == 0x7E4) {
+      // ContentSigKeyID
+      delete[] encryption->sig_key_id;
+      encryption->sig_key_id = NULL;
+      encryption->sig_key_id_len = 0;
+
+      if (size <= 0)
+        return E_FILE_FORMAT_INVALID;
+
+      const size_t buflen = static_cast<size_t>(size);
+      typedef unsigned char* buf_t;
+      const buf_t buf = new (std::nothrow) unsigned char[buflen];
+      if (buf == NULL)
+        return -1;
+
+      const int read_status = pReader->Read(pos, buflen, buf);
+      if (read_status) {
+        delete [] buf;
+        return status;
+      }
+
+      encryption->sig_key_id = buf;
+      encryption->sig_key_id_len = buflen;
+    } else if (id == 0x7E5) {
+      // ContentSigAlgo
+      encryption->sig_algo = UnserializeUInt(pReader, pos, size);
+    } else if (id == 0x7E6) {
+      // ContentSigHashAlgo
+      encryption->sig_hash_algo = UnserializeUInt(pReader, pos, size);
+    } else if (id == 0x7E7) {
+      // ContentEncAESSettings
+      const long status = ParseContentEncAESSettingsEntry(
+          pos,
+          size,
+          pReader,
+          &encryption->aes_settings);
+      if (status)
+        return status;
+    }
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  return 0;
+}
+
+Track::Track(
+    Segment* pSegment,
+    long long element_start,
+    long long element_size) :
+    m_pSegment(pSegment),
+    m_element_start(element_start),
+    m_element_size(element_size),
+    content_encoding_entries_(NULL),
+    content_encoding_entries_end_(NULL)
+{
+}
+
+Track::~Track()
+{
+    Info& info = const_cast<Info&>(m_info);
+    info.Clear();
+
+    ContentEncoding** i = content_encoding_entries_;
+    ContentEncoding** const j = content_encoding_entries_end_;
+
+    while (i != j) {
+        ContentEncoding* const encoding = *i++;
+        delete encoding;
+    }
+
+    delete [] content_encoding_entries_;
+}
+
+long Track::Create(
+    Segment* pSegment,
+    const Info& info,
+    long long element_start,
+    long long element_size,
+    Track*& pResult)
+{
+    if (pResult)
+        return -1;
+
+    Track* const pTrack = new (std::nothrow) Track(pSegment,
+                                                   element_start,
+                                                   element_size);
+
+    if (pTrack == NULL)
+        return -1;  //generic error
+
+    const int status = info.Copy(pTrack->m_info);
+
+    if (status)  // error
+    {
+        delete pTrack;
+        return status;
+    }
+
+    pResult = pTrack;
+    return 0;  //success
+}
+
+Track::Info::Info():
+    uid(0),
+    defaultDuration(0),
+    codecDelay(0),
+    seekPreRoll(0),
+    nameAsUTF8(NULL),
+    language(NULL),
+    codecId(NULL),
+    codecNameAsUTF8(NULL),
+    codecPrivate(NULL),
+    codecPrivateSize(0),
+    lacing(false)
+{
+}
+
+Track::Info::~Info()
+{
+    Clear();
+}
+
+void Track::Info::Clear()
+{
+    delete[] nameAsUTF8;
+    nameAsUTF8 = NULL;
+
+    delete[] language;
+    language = NULL;
+
+    delete[] codecId;
+    codecId = NULL;
+
+    delete[] codecPrivate;
+    codecPrivate = NULL;
+    codecPrivateSize = 0;
+
+    delete[] codecNameAsUTF8;
+    codecNameAsUTF8 = NULL;
+}
+
+int Track::Info::CopyStr(char* Info::*str, Info& dst_) const
+{
+    if (str == static_cast<char* Info::*>(NULL))
+        return -1;
+
+    char*& dst = dst_.*str;
+
+    if (dst)  //should be NULL already
+        return -1;
+
+    const char* const src = this->*str;
+
+    if (src == NULL)
+        return 0;
+
+    const size_t len = strlen(src);
+
+    dst = new (std::nothrow) char[len+1];
+
+    if (dst == NULL)
+        return -1;
+
+    strcpy(dst, src);
+
+    return 0;
+}
+
+
+int Track::Info::Copy(Info& dst) const
+{
+    if (&dst == this)
+        return 0;
+
+    dst.type = type;
+    dst.number = number;
+    dst.defaultDuration = defaultDuration;
+    dst.codecDelay = codecDelay;
+    dst.seekPreRoll = seekPreRoll;
+    dst.uid = uid;
+    dst.lacing = lacing;
+    dst.settings = settings;
+
+    //We now copy the string member variables from src to dst.
+    //This involves memory allocation so in principle the operation
+    //can fail (indeed, that's why we have Info::Copy), so we must
+    //report this to the caller.  An error return from this function
+    //therefore implies that the copy was only partially successful.
+
+    if (int status = CopyStr(&Info::nameAsUTF8, dst))
+        return status;
+
+    if (int status = CopyStr(&Info::language, dst))
+        return status;
+
+    if (int status = CopyStr(&Info::codecId, dst))
+        return status;
+
+    if (int status = CopyStr(&Info::codecNameAsUTF8, dst))
+        return status;
+
+    if (codecPrivateSize > 0)
+    {
+        if (codecPrivate == NULL)
+            return -1;
+
+        if (dst.codecPrivate)
+            return -1;
+
+        if (dst.codecPrivateSize != 0)
+            return -1;
+
+        dst.codecPrivate = new (std::nothrow) unsigned char[codecPrivateSize];
+
+        if (dst.codecPrivate == NULL)
+            return -1;
+
+        memcpy(dst.codecPrivate, codecPrivate, codecPrivateSize);
+        dst.codecPrivateSize = codecPrivateSize;
+    }
+
+    return 0;
+}
+
+const BlockEntry* Track::GetEOS() const
+{
+    return &m_eos;
+}
+
+long Track::GetType() const
+{
+    return m_info.type;
+}
+
+long Track::GetNumber() const
+{
+    return m_info.number;
+}
+
+unsigned long long Track::GetUid() const
+{
+    return m_info.uid;
+}
+
+const char* Track::GetNameAsUTF8() const
+{
+    return m_info.nameAsUTF8;
+}
+
+const char* Track::GetLanguage() const
+{
+    return m_info.language;
+}
+
+const char* Track::GetCodecNameAsUTF8() const
+{
+    return m_info.codecNameAsUTF8;
+}
+
+
+const char* Track::GetCodecId() const
+{
+    return m_info.codecId;
+}
+
+const unsigned char* Track::GetCodecPrivate(size_t& size) const
+{
+    size = m_info.codecPrivateSize;
+    return m_info.codecPrivate;
+}
+
+
+bool Track::GetLacing() const
+{
+    return m_info.lacing;
+}
+
+unsigned long long Track::GetDefaultDuration() const
+{
+    return m_info.defaultDuration;
+}
+
+unsigned long long Track::GetCodecDelay() const
+{
+    return m_info.codecDelay;
+}
+
+unsigned long long Track::GetSeekPreRoll() const
+{
+    return m_info.seekPreRoll;
+}
+
+long Track::GetFirst(const BlockEntry*& pBlockEntry) const
+{
+    const Cluster* pCluster = m_pSegment->GetFirst();
+
+    for (int i = 0; ; )
+    {
+        if (pCluster == NULL)
+        {
+            pBlockEntry = GetEOS();
+            return 1;
+        }
+
+        if (pCluster->EOS())
+        {
+#if 0
+            if (m_pSegment->Unparsed() <= 0)  //all clusters have been loaded
+            {
+                pBlockEntry = GetEOS();
+                return 1;
+            }
+#else
+            if (m_pSegment->DoneParsing())
+            {
+                pBlockEntry = GetEOS();
+                return 1;
+            }
+#endif
+
+            pBlockEntry = 0;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long status = pCluster->GetFirst(pBlockEntry);
+
+        if (status < 0)  //error
+            return status;
+
+        if (pBlockEntry == 0)  //empty cluster
+        {
+            pCluster = m_pSegment->GetNext(pCluster);
+            continue;
+        }
+
+        for (;;)
+        {
+            const Block* const pBlock = pBlockEntry->GetBlock();
+            assert(pBlock);
+
+            const long long tn = pBlock->GetTrackNumber();
+
+            if ((tn == m_info.number) && VetEntry(pBlockEntry))
+                return 0;
+
+            const BlockEntry* pNextEntry;
+
+            status = pCluster->GetNext(pBlockEntry, pNextEntry);
+
+            if (status < 0)  //error
+                return status;
+
+            if (pNextEntry == 0)
+                break;
+
+            pBlockEntry = pNextEntry;
+        }
+
+        ++i;
+
+        if (i >= 100)
+            break;
+
+        pCluster = m_pSegment->GetNext(pCluster);
+    }
+
+    //NOTE: if we get here, it means that we didn't find a block with
+    //a matching track number.  We interpret that as an error (which
+    //might be too conservative).
+
+    pBlockEntry = GetEOS();  //so we can return a non-NULL value
+    return 1;
+}
+
+
+long Track::GetNext(
+    const BlockEntry* pCurrEntry,
+    const BlockEntry*& pNextEntry) const
+{
+    assert(pCurrEntry);
+    assert(!pCurrEntry->EOS());  //?
+
+    const Block* const pCurrBlock = pCurrEntry->GetBlock();
+    assert(pCurrBlock && pCurrBlock->GetTrackNumber() == m_info.number);
+    if (!pCurrBlock || pCurrBlock->GetTrackNumber() != m_info.number)
+        return -1;
+
+    const Cluster* pCluster = pCurrEntry->GetCluster();
+    assert(pCluster);
+    assert(!pCluster->EOS());
+
+    long status = pCluster->GetNext(pCurrEntry, pNextEntry);
+
+    if (status < 0)  //error
+        return status;
+
+    for (int i = 0; ; )
+    {
+        while (pNextEntry)
+        {
+            const Block* const pNextBlock = pNextEntry->GetBlock();
+            assert(pNextBlock);
+
+            if (pNextBlock->GetTrackNumber() == m_info.number)
+                return 0;
+
+            pCurrEntry = pNextEntry;
+
+            status = pCluster->GetNext(pCurrEntry, pNextEntry);
+
+            if (status < 0) //error
+                return status;
+        }
+
+        pCluster = m_pSegment->GetNext(pCluster);
+
+        if (pCluster == NULL)
+        {
+            pNextEntry = GetEOS();
+            return 1;
+        }
+
+        if (pCluster->EOS())
+        {
+#if 0
+            if (m_pSegment->Unparsed() <= 0)   //all clusters have been loaded
+            {
+                pNextEntry = GetEOS();
+                return 1;
+            }
+#else
+            if (m_pSegment->DoneParsing())
+            {
+                pNextEntry = GetEOS();
+                return 1;
+            }
+#endif
+
+            //TODO: there is a potential O(n^2) problem here: we tell the
+            //caller to (pre)load another cluster, which he does, but then he
+            //calls GetNext again, which repeats the same search.  This is
+            //a pathological case, since the only way it can happen is if
+            //there exists a long sequence of clusters none of which contain a
+            // block from this track.  One way around this problem is for the
+            //caller to be smarter when he loads another cluster: don't call
+            //us back until you have a cluster that contains a block from this
+            //track. (Of course, that's not cheap either, since our caller
+            //would have to scan the each cluster as it's loaded, so that
+            //would just push back the problem.)
+
+            pNextEntry = NULL;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        status = pCluster->GetFirst(pNextEntry);
+
+        if (status < 0)  //error
+            return status;
+
+        if (pNextEntry == NULL)  //empty cluster
+            continue;
+
+        ++i;
+
+        if (i >= 100)
+            break;
+    }
+
+    //NOTE: if we get here, it means that we didn't find a block with
+    //a matching track number after lots of searching, so we give
+    //up trying.
+
+    pNextEntry = GetEOS();  //so we can return a non-NULL value
+    return 1;
+}
+
+bool Track::VetEntry(const BlockEntry* pBlockEntry) const
+{
+    assert(pBlockEntry);
+    const Block* const pBlock = pBlockEntry->GetBlock();
+    assert(pBlock);
+    assert(pBlock->GetTrackNumber() == m_info.number);
+    if (!pBlock || pBlock->GetTrackNumber() != m_info.number)
+        return false;
+
+    // This function is used during a seek to determine whether the
+    // frame is a valid seek target.  This default function simply
+    // returns true, which means all frames are valid seek targets.
+    // It gets overridden by the VideoTrack class, because only video
+    // keyframes can be used as seek target.
+
+    return true;
+}
+
+long Track::Seek(
+    long long time_ns,
+    const BlockEntry*& pResult) const
+{
+    const long status = GetFirst(pResult);
+
+    if (status < 0)  //buffer underflow, etc
+        return status;
+
+    assert(pResult);
+
+    if (pResult->EOS())
+        return 0;
+
+    const Cluster* pCluster = pResult->GetCluster();
+    assert(pCluster);
+    assert(pCluster->GetIndex() >= 0);
+
+    if (time_ns <= pResult->GetBlock()->GetTime(pCluster))
+        return 0;
+
+    Cluster** const clusters = m_pSegment->m_clusters;
+    assert(clusters);
+
+    const long count = m_pSegment->GetCount();  //loaded only, not preloaded
+    assert(count > 0);
+
+    Cluster** const i = clusters + pCluster->GetIndex();
+    assert(i);
+    assert(*i == pCluster);
+    assert(pCluster->GetTime() <= time_ns);
+
+    Cluster** const j = clusters + count;
+
+    Cluster** lo = i;
+    Cluster** hi = j;
+
+    while (lo < hi)
+    {
+        //INVARIANT:
+        //[i, lo) <= time_ns
+        //[lo, hi) ?
+        //[hi, j)  > time_ns
+
+        Cluster** const mid = lo + (hi - lo) / 2;
+        assert(mid < hi);
+
+        pCluster = *mid;
+        assert(pCluster);
+        assert(pCluster->GetIndex() >= 0);
+        assert(pCluster->GetIndex() == long(mid - m_pSegment->m_clusters));
+
+        const long long t = pCluster->GetTime();
+
+        if (t <= time_ns)
+            lo = mid + 1;
+        else
+            hi = mid;
+
+        assert(lo <= hi);
+    }
+
+    assert(lo == hi);
+    assert(lo > i);
+    assert(lo <= j);
+
+    while (lo > i)
+    {
+        pCluster = *--lo;
+        assert(pCluster);
+        assert(pCluster->GetTime() <= time_ns);
+
+        pResult = pCluster->GetEntry(this);
+
+        if ((pResult != 0) && !pResult->EOS())
+            return 0;
+
+        //landed on empty cluster (no entries)
+    }
+
+    pResult = GetEOS();  //weird
+    return 0;
+}
+
+const ContentEncoding*
+Track::GetContentEncodingByIndex(unsigned long idx) const {
+  const ptrdiff_t count =
+      content_encoding_entries_end_ - content_encoding_entries_;
+  assert(count >= 0);
+
+  if (idx >= static_cast<unsigned long>(count))
+    return NULL;
+
+  return content_encoding_entries_[idx];
+}
+
+unsigned long Track::GetContentEncodingCount() const {
+  const ptrdiff_t count =
+      content_encoding_entries_end_ - content_encoding_entries_;
+  assert(count >= 0);
+
+  return static_cast<unsigned long>(count);
+}
+
+long Track::ParseContentEncodingsEntry(long long start, long long size) {
+  IMkvReader* const pReader = m_pSegment->m_pReader;
+  assert(pReader);
+
+  long long pos = start;
+  const long long stop = start + size;
+
+  // Count ContentEncoding elements.
+  int count = 0;
+  while (pos < stop) {
+    long long id, size;
+    const long status = ParseElementHeader(pReader,
+                                           pos,
+                                           stop,
+                                           id,
+                                           size);
+    if (status < 0)  //error
+      return status;
+
+
+    //pos now designates start of element
+    if (id == 0x2240)  // ContentEncoding ID
+      ++count;
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  if (count <= 0)
+    return -1;
+
+  content_encoding_entries_ = new (std::nothrow) ContentEncoding*[count];
+  if (!content_encoding_entries_)
+    return -1;
+
+  content_encoding_entries_end_ = content_encoding_entries_;
+
+  pos = start;
+  while (pos < stop) {
+    long long id, size;
+    long status = ParseElementHeader(pReader,
+                                     pos,
+                                     stop,
+                                     id,
+                                     size);
+    if (status < 0)  //error
+      return status;
+
+    //pos now designates start of element
+    if (id == 0x2240) { // ContentEncoding ID
+      ContentEncoding* const content_encoding =
+          new (std::nothrow) ContentEncoding();
+      if (!content_encoding)
+        return -1;
+
+      status = content_encoding->ParseContentEncodingEntry(pos,
+                                                           size,
+                                                           pReader);
+      if (status) {
+        delete content_encoding;
+        return status;
+      }
+
+      *content_encoding_entries_end_++ = content_encoding;
+    }
+
+    pos += size;  //consume payload
+    assert(pos <= stop);
+  }
+
+  assert(pos == stop);
+
+  return 0;
+}
+
+Track::EOSBlock::EOSBlock() :
+    BlockEntry(NULL, LONG_MIN)
+{
+}
+
+BlockEntry::Kind Track::EOSBlock::GetKind() const
+{
+    return kBlockEOS;
+}
+
+
+const Block* Track::EOSBlock::GetBlock() const
+{
+    return NULL;
+}
+
+
+VideoTrack::VideoTrack(
+    Segment* pSegment,
+    long long element_start,
+    long long element_size) :
+    Track(pSegment, element_start, element_size)
+{
+}
+
+
+long VideoTrack::Parse(
+    Segment* pSegment,
+    const Info& info,
+    long long element_start,
+    long long element_size,
+    VideoTrack*& pResult)
+{
+    if (pResult)
+        return -1;
+
+    if (info.type != Track::kVideo)
+        return -1;
+
+    long long width = 0;
+    long long height = 0;
+    double rate = 0.0;
+
+    IMkvReader* const pReader = pSegment->m_pReader;
+
+    const Settings& s = info.settings;
+    assert(s.start >= 0);
+    assert(s.size >= 0);
+
+    long long pos = s.start;
+    assert(pos >= 0);
+
+    const long long stop = pos + s.size;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (id == 0x30)  //pixel width
+        {
+            width = UnserializeUInt(pReader, pos, size);
+
+            if (width <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x3A)  //pixel height
+        {
+            height = UnserializeUInt(pReader, pos, size);
+
+            if (height <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x0383E3)  //frame rate
+        {
+            const long status = UnserializeFloat(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    rate);
+
+            if (status < 0)
+                return status;
+
+            if (rate <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    VideoTrack* const pTrack = new (std::nothrow) VideoTrack(pSegment,
+                                                             element_start,
+                                                             element_size);
+
+    if (pTrack == NULL)
+        return -1;  //generic error
+
+    const int status = info.Copy(pTrack->m_info);
+
+    if (status)  // error
+    {
+        delete pTrack;
+        return status;
+    }
+
+    pTrack->m_width = width;
+    pTrack->m_height = height;
+    pTrack->m_rate = rate;
+
+    pResult = pTrack;
+    return 0;  //success
+}
+
+
+bool VideoTrack::VetEntry(const BlockEntry* pBlockEntry) const
+{
+    return Track::VetEntry(pBlockEntry) && pBlockEntry->GetBlock()->IsKey();
+}
+
+long VideoTrack::Seek(
+    long long time_ns,
+    const BlockEntry*& pResult) const
+{
+    const long status = GetFirst(pResult);
+
+    if (status < 0)  //buffer underflow, etc
+        return status;
+
+    assert(pResult);
+
+    if (pResult->EOS())
+        return 0;
+
+    const Cluster* pCluster = pResult->GetCluster();
+    assert(pCluster);
+    assert(pCluster->GetIndex() >= 0);
+
+    if (time_ns <= pResult->GetBlock()->GetTime(pCluster))
+        return 0;
+
+    Cluster** const clusters = m_pSegment->m_clusters;
+    assert(clusters);
+
+    const long count = m_pSegment->GetCount();  //loaded only, not pre-loaded
+    assert(count > 0);
+
+    Cluster** const i = clusters + pCluster->GetIndex();
+    assert(i);
+    assert(*i == pCluster);
+    assert(pCluster->GetTime() <= time_ns);
+
+    Cluster** const j = clusters + count;
+
+    Cluster** lo = i;
+    Cluster** hi = j;
+
+    while (lo < hi)
+    {
+        //INVARIANT:
+        //[i, lo) <= time_ns
+        //[lo, hi) ?
+        //[hi, j)  > time_ns
+
+        Cluster** const mid = lo + (hi - lo) / 2;
+        assert(mid < hi);
+
+        pCluster = *mid;
+        assert(pCluster);
+        assert(pCluster->GetIndex() >= 0);
+        assert(pCluster->GetIndex() == long(mid - m_pSegment->m_clusters));
+
+        const long long t = pCluster->GetTime();
+
+        if (t <= time_ns)
+            lo = mid + 1;
+        else
+            hi = mid;
+
+        assert(lo <= hi);
+    }
+
+    assert(lo == hi);
+    assert(lo > i);
+    assert(lo <= j);
+
+    pCluster = *--lo;
+    assert(pCluster);
+    assert(pCluster->GetTime() <= time_ns);
+
+    pResult = pCluster->GetEntry(this, time_ns);
+
+    if ((pResult != 0) && !pResult->EOS())  //found a keyframe
+        return 0;
+
+    while (lo != i)
+    {
+        pCluster = *--lo;
+        assert(pCluster);
+        assert(pCluster->GetTime() <= time_ns);
+
+#if 0
+        //TODO:
+        //We need to handle the case when a cluster
+        //contains multiple keyframes.  Simply returning
+        //the largest keyframe on the cluster isn't
+        //good enough.
+        pResult = pCluster->GetMaxKey(this);
+#else
+        pResult = pCluster->GetEntry(this, time_ns);
+#endif
+
+        if ((pResult != 0) && !pResult->EOS())
+            return 0;
+    }
+
+    //weird: we're on the first cluster, but no keyframe found
+    //should never happen but we must return something anyway
+
+    pResult = GetEOS();
+    return 0;
+}
+
+
+long long VideoTrack::GetWidth() const
+{
+    return m_width;
+}
+
+
+long long VideoTrack::GetHeight() const
+{
+    return m_height;
+}
+
+
+double VideoTrack::GetFrameRate() const
+{
+    return m_rate;
+}
+
+
+AudioTrack::AudioTrack(
+    Segment* pSegment,
+    long long element_start,
+    long long element_size) :
+    Track(pSegment, element_start, element_size)
+{
+}
+
+
+long AudioTrack::Parse(
+    Segment* pSegment,
+    const Info& info,
+    long long element_start,
+    long long element_size,
+    AudioTrack*& pResult)
+{
+    if (pResult)
+        return -1;
+
+    if (info.type != Track::kAudio)
+        return -1;
+
+    IMkvReader* const pReader = pSegment->m_pReader;
+
+    const Settings& s = info.settings;
+    assert(s.start >= 0);
+    assert(s.size >= 0);
+
+    long long pos = s.start;
+    assert(pos >= 0);
+
+    const long long stop = pos + s.size;
+
+    double rate = 8000.0;  // MKV default
+    long long channels = 1;
+    long long bit_depth = 0;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (id == 0x35)  //Sample Rate
+        {
+            status = UnserializeFloat(pReader, pos, size, rate);
+
+            if (status < 0)
+                return status;
+
+            if (rate <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x1F)  //Channel Count
+        {
+            channels = UnserializeUInt(pReader, pos, size);
+
+            if (channels <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x2264)  //Bit Depth
+        {
+            bit_depth = UnserializeUInt(pReader, pos, size);
+
+            if (bit_depth <= 0)
+                return E_FILE_FORMAT_INVALID;
+        }
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    AudioTrack* const pTrack = new (std::nothrow) AudioTrack(pSegment,
+                                                             element_start,
+                                                             element_size);
+
+    if (pTrack == NULL)
+        return -1;  //generic error
+
+    const int status = info.Copy(pTrack->m_info);
+
+    if (status)
+    {
+        delete pTrack;
+        return status;
+    }
+
+    pTrack->m_rate = rate;
+    pTrack->m_channels = channels;
+    pTrack->m_bitDepth = bit_depth;
+
+    pResult = pTrack;
+    return 0;  //success
+}
+
+
+double AudioTrack::GetSamplingRate() const
+{
+    return m_rate;
+}
+
+
+long long AudioTrack::GetChannels() const
+{
+    return m_channels;
+}
+
+long long AudioTrack::GetBitDepth() const
+{
+    return m_bitDepth;
+}
+
+Tracks::Tracks(
+    Segment* pSegment,
+    long long start,
+    long long size_,
+    long long element_start,
+    long long element_size) :
+    m_pSegment(pSegment),
+    m_start(start),
+    m_size(size_),
+    m_element_start(element_start),
+    m_element_size(element_size),
+    m_trackEntries(NULL),
+    m_trackEntriesEnd(NULL)
+{
+}
+
+
+long Tracks::Parse()
+{
+    assert(m_trackEntries == NULL);
+    assert(m_trackEntriesEnd == NULL);
+
+    const long long stop = m_start + m_size;
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    int count = 0;
+    long long pos = m_start;
+
+    while (pos < stop)
+    {
+        long long id, size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (size == 0)  //weird
+            continue;
+
+        if (id == 0x2E)  //TrackEntry ID
+            ++count;
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    if (count <= 0)
+        return 0;  //success
+
+    m_trackEntries = new (std::nothrow) Track*[count];
+
+    if (m_trackEntries == NULL)
+        return -1;
+
+    m_trackEntriesEnd = m_trackEntries;
+
+    pos = m_start;
+
+    while (pos < stop)
+    {
+        const long long element_start = pos;
+
+        long long id, payload_size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                stop,
+                                id,
+                                payload_size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (payload_size == 0)  //weird
+            continue;
+
+        const long long payload_stop = pos + payload_size;
+        assert(payload_stop <= stop);  //checked in ParseElement
+
+        const long long element_size = payload_stop - element_start;
+
+        if (id == 0x2E)  //TrackEntry ID
+        {
+            Track*& pTrack = *m_trackEntriesEnd;
+            pTrack = NULL;
+
+            const long status = ParseTrackEntry(
+                                    pos,
+                                    payload_size,
+                                    element_start,
+                                    element_size,
+                                    pTrack);
+
+            if (status)
+                return status;
+
+            if (pTrack)
+                ++m_trackEntriesEnd;
+        }
+
+        pos = payload_stop;
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+
+    return 0;  //success
+}
+
+
+unsigned long Tracks::GetTracksCount() const
+{
+    const ptrdiff_t result = m_trackEntriesEnd - m_trackEntries;
+    assert(result >= 0);
+
+    return static_cast<unsigned long>(result);
+}
+
+long Tracks::ParseTrackEntry(
+    long long track_start,
+    long long track_size,
+    long long element_start,
+    long long element_size,
+    Track*& pResult) const
+{
+    if (pResult)
+        return -1;
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long pos = track_start;
+    const long long track_stop = track_start + track_size;
+
+    Track::Info info;
+
+    info.type = 0;
+    info.number = 0;
+    info.uid = 0;
+    info.defaultDuration = 0;
+
+    Track::Settings v;
+    v.start = -1;
+    v.size = -1;
+
+    Track::Settings a;
+    a.start = -1;
+    a.size = -1;
+
+    Track::Settings e;  //content_encodings_settings;
+    e.start = -1;
+    e.size = -1;
+
+    long long lacing = 1;  //default is true
+
+    while (pos < track_stop)
+    {
+        long long id, size;
+
+        const long status = ParseElementHeader(
+                                pReader,
+                                pos,
+                                track_stop,
+                                id,
+                                size);
+
+        if (status < 0)  //error
+            return status;
+
+        if (size < 0)
+            return E_FILE_FORMAT_INVALID;
+
+        const long long start = pos;
+
+        if (id == 0x60)  // VideoSettings ID
+        {
+            v.start = start;
+            v.size = size;
+        }
+        else if (id == 0x61)  // AudioSettings ID
+        {
+            a.start = start;
+            a.size = size;
+        }
+        else if (id == 0x2D80) // ContentEncodings ID
+        {
+            e.start = start;
+            e.size = size;
+        }
+        else if (id == 0x33C5)  //Track UID
+        {
+            if (size > 8)
+                return E_FILE_FORMAT_INVALID;
+
+            info.uid = 0;
+
+            long long pos_ = start;
+            const long long pos_end = start + size;
+
+            while (pos_ != pos_end)
+            {
+                unsigned char b;
+
+                const int status = pReader->Read(pos_, 1, &b);
+
+                if (status)
+                    return status;
+
+                info.uid <<= 8;
+                info.uid |= b;
+
+                ++pos_;
+            }
+        }
+        else if (id == 0x57)  //Track Number
+        {
+            const long long num = UnserializeUInt(pReader, pos, size);
+
+            if ((num <= 0) || (num > 127))
+                return E_FILE_FORMAT_INVALID;
+
+            info.number = static_cast<long>(num);
+        }
+        else if (id == 0x03)  //Track Type
+        {
+            const long long type = UnserializeUInt(pReader, pos, size);
+
+            if ((type <= 0) || (type > 254))
+                return E_FILE_FORMAT_INVALID;
+
+            info.type = static_cast<long>(type);
+        }
+        else if (id == 0x136E)  //Track Name
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    info.nameAsUTF8);
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x02B59C)  //Track Language
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    info.language);
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x03E383)  //Default Duration
+        {
+            const long long duration = UnserializeUInt(pReader, pos, size);
+
+            if (duration < 0)
+                return E_FILE_FORMAT_INVALID;
+
+            info.defaultDuration = static_cast<unsigned long long>(duration);
+        }
+        else if (id == 0x06)  //CodecID
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    info.codecId);
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x1C)  //lacing
+        {
+            lacing = UnserializeUInt(pReader, pos, size);
+
+            if ((lacing < 0) || (lacing > 1))
+                return E_FILE_FORMAT_INVALID;
+        }
+        else if (id == 0x23A2)  //Codec Private
+        {
+            delete[] info.codecPrivate;
+            info.codecPrivate = NULL;
+            info.codecPrivateSize = 0;
+
+            const size_t buflen = static_cast<size_t>(size);
+
+            if (buflen)
+            {
+                typedef unsigned char* buf_t;
+
+                const buf_t buf = new (std::nothrow) unsigned char[buflen];
+
+                if (buf == NULL)
+                    return -1;
+
+                const int status = pReader->Read(pos, buflen, buf);
+
+                if (status)
+                {
+                    delete[] buf;
+                    return status;
+                }
+
+                info.codecPrivate = buf;
+                info.codecPrivateSize = buflen;
+            }
+        }
+        else if (id == 0x058688)  //Codec Name
+        {
+            const long status = UnserializeString(
+                                    pReader,
+                                    pos,
+                                    size,
+                                    info.codecNameAsUTF8);
+
+            if (status)
+                return status;
+        }
+        else if (id == 0x16AA)  //Codec Delay
+        {
+            info.codecDelay = UnserializeUInt(pReader, pos, size);
+
+        }
+        else if (id == 0x16BB) //Seek Pre Roll
+        {
+            info.seekPreRoll = UnserializeUInt(pReader, pos, size);
+        }
+
+        pos += size;  //consume payload
+        assert(pos <= track_stop);
+    }
+
+    assert(pos == track_stop);
+
+    if (info.number <= 0)  //not specified
+        return E_FILE_FORMAT_INVALID;
+
+    if (GetTrackByNumber(info.number))
+        return E_FILE_FORMAT_INVALID;
+
+    if (info.type <= 0)  //not specified
+        return E_FILE_FORMAT_INVALID;
+
+    info.lacing = (lacing > 0) ? true : false;
+
+    if (info.type == Track::kVideo)
+    {
+        if (v.start < 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (a.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        info.settings = v;
+
+        VideoTrack* pTrack = NULL;
+
+        const long status = VideoTrack::Parse(m_pSegment,
+                                              info,
+                                              element_start,
+                                              element_size,
+                                              pTrack);
+
+        if (status)
+            return status;
+
+        pResult = pTrack;
+        assert(pResult);
+
+        if (e.start >= 0)
+            pResult->ParseContentEncodingsEntry(e.start, e.size);
+    }
+    else if (info.type == Track::kAudio)
+    {
+        if (a.start < 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (v.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        info.settings = a;
+
+        AudioTrack* pTrack = NULL;
+
+        const long status = AudioTrack::Parse(m_pSegment,
+                                              info,
+                                              element_start,
+                                              element_size,
+                                              pTrack);
+
+        if (status)
+            return status;
+
+        pResult = pTrack;
+        assert(pResult);
+
+        if (e.start >= 0)
+            pResult->ParseContentEncodingsEntry(e.start, e.size);
+    }
+    else
+    {
+        // neither video nor audio - probably metadata or subtitles
+
+        if (a.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (v.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (e.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        info.settings.start = -1;
+        info.settings.size = 0;
+
+        Track* pTrack = NULL;
+
+        const long status = Track::Create(m_pSegment,
+                                          info,
+                                          element_start,
+                                          element_size,
+                                          pTrack);
+
+        if (status)
+            return status;
+
+        pResult = pTrack;
+        assert(pResult);
+    }
+
+    return 0;  //success
+}
+
+
+Tracks::~Tracks()
+{
+    Track** i = m_trackEntries;
+    Track** const j = m_trackEntriesEnd;
+
+    while (i != j)
+    {
+        Track* const pTrack = *i++;
+        delete pTrack;
+    }
+
+    delete[] m_trackEntries;
+}
+
+const Track* Tracks::GetTrackByNumber(long tn) const
+{
+    if (tn < 0)
+        return NULL;
+
+    Track** i = m_trackEntries;
+    Track** const j = m_trackEntriesEnd;
+
+    while (i != j)
+    {
+        Track* const pTrack = *i++;
+
+        if (pTrack == NULL)
+            continue;
+
+        if (tn == pTrack->GetNumber())
+            return pTrack;
+    }
+
+    return NULL;  //not found
+}
+
+
+const Track* Tracks::GetTrackByIndex(unsigned long idx) const
+{
+    const ptrdiff_t count = m_trackEntriesEnd - m_trackEntries;
+
+    if (idx >= static_cast<unsigned long>(count))
+         return NULL;
+
+    return m_trackEntries[idx];
+}
+
+#if 0
+long long Cluster::Unparsed() const
+{
+    if (m_timecode < 0)  //not even partially loaded
+        return LLONG_MAX;
+
+    assert(m_pos >= m_element_start);
+    //assert(m_element_size > m_size);
+
+    const long long element_stop = m_element_start + m_element_size;
+    assert(m_pos <= element_stop);
+
+    const long long result = element_stop - m_pos;
+    assert(result >= 0);
+
+    return result;
+}
+#endif
+
+
+long Cluster::Load(long long& pos, long& len) const
+{
+    assert(m_pSegment);
+    assert(m_pos >= m_element_start);
+
+    if (m_timecode >= 0)  //at least partially loaded
+        return 0;
+
+    assert(m_pos == m_element_start);
+    assert(m_element_size < 0);
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long total, avail;
+
+    const int status = pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+    assert((total < 0) || (m_pos <= total));  //TODO: verify this
+
+    pos = m_pos;
+
+    long long cluster_size = -1;
+
+    {
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error or underflow
+            return static_cast<long>(result);
+
+        if (result > 0)  //underflow (weird)
+            return E_BUFFER_NOT_FULL;
+
+        //if ((pos + len) > segment_stop)
+        //    return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id_ = ReadUInt(pReader, pos, len);
+
+        if (id_ < 0)  //error
+            return static_cast<long>(id_);
+
+        if (id_ != 0x0F43B675)  //Cluster ID
+            return E_FILE_FORMAT_INVALID;
+
+        pos += len;  //consume id
+
+        //read cluster size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        //if ((pos + len) > segment_stop)
+        //    return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(cluster_size);
+
+        if (size == 0)
+            return E_FILE_FORMAT_INVALID;  //TODO: verify this
+
+        pos += len;  //consume length of size of element
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size != unknown_size)
+            cluster_size = size;
+    }
+
+    //pos points to start of payload
+
+#if 0
+    len = static_cast<long>(size_);
+
+    if (cluster_stop > avail)
+        return E_BUFFER_NOT_FULL;
+#endif
+
+    long long timecode = -1;
+    long long new_pos = -1;
+    bool bBlock = false;
+
+    long long cluster_stop = (cluster_size < 0) ? -1 : pos + cluster_size;
+
+    for (;;)
+    {
+        if ((cluster_stop >= 0) && (pos >= cluster_stop))
+            break;
+
+        //Parse ID
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id = ReadUInt(pReader, pos, len);
+
+        if (id < 0) //error
+            return static_cast<long>(id);
+
+        if (id == 0)
+            return E_FILE_FORMAT_INVALID;
+
+        //This is the distinguished set of ID's we use to determine
+        //that we have exhausted the sub-element's inside the cluster
+        //whose ID we parsed earlier.
+
+        if (id == 0x0F43B675)  //Cluster ID
+            break;
+
+        if (id == 0x0C53BB6B)  //Cues ID
+            break;
+
+        pos += len;  //consume ID field
+
+        //Parse Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;
+
+        pos += len;  //consume size field
+
+        if ((cluster_stop >= 0) && (pos > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        //pos now points to start of payload
+
+        if (size == 0)  //weird
+            continue;
+
+        if ((cluster_stop >= 0) && ((pos + size) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if (id == 0x67)  //TimeCode ID
+        {
+            len = static_cast<long>(size);
+
+            if ((pos + size) > avail)
+                return E_BUFFER_NOT_FULL;
+
+            timecode = UnserializeUInt(pReader, pos, size);
+
+            if (timecode < 0)  //error (or underflow)
+                return static_cast<long>(timecode);
+
+            new_pos = pos + size;
+
+            if (bBlock)
+                break;
+        }
+        else if (id == 0x20)  //BlockGroup ID
+        {
+            bBlock = true;
+            break;
+        }
+        else if (id == 0x23)  //SimpleBlock ID
+        {
+            bBlock = true;
+            break;
+        }
+
+        pos += size;  //consume payload
+        assert((cluster_stop < 0) || (pos <= cluster_stop));
+    }
+
+    assert((cluster_stop < 0) || (pos <= cluster_stop));
+
+    if (timecode < 0)  //no timecode found
+        return E_FILE_FORMAT_INVALID;
+
+    if (!bBlock)
+        return E_FILE_FORMAT_INVALID;
+
+    m_pos = new_pos;  //designates position just beyond timecode payload
+    m_timecode = timecode;  // m_timecode >= 0 means we're partially loaded
+
+    if (cluster_size >= 0)
+        m_element_size = cluster_stop - m_element_start;
+
+    return 0;
+}
+
+
+long Cluster::Parse(long long& pos, long& len) const
+{
+    long status = Load(pos, len);
+
+    if (status < 0)
+        return status;
+
+    assert(m_pos >= m_element_start);
+    assert(m_timecode >= 0);
+    //assert(m_size > 0);
+    //assert(m_element_size > m_size);
+
+    const long long cluster_stop =
+        (m_element_size < 0) ? -1 : m_element_start + m_element_size;
+
+    if ((cluster_stop >= 0) && (m_pos >= cluster_stop))
+        return 1;  //nothing else to do
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long total, avail;
+
+    status = pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    pos = m_pos;
+
+    for (;;)
+    {
+        if ((cluster_stop >= 0) && (pos >= cluster_stop))
+            break;
+
+        if ((total >= 0) && (pos >= total))
+        {
+            if (m_element_size < 0)
+                m_element_size = pos - m_element_start;
+
+            break;
+        }
+
+        //Parse ID
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id = ReadUInt(pReader, pos, len);
+
+        if (id < 0) //error
+            return static_cast<long>(id);
+
+        if (id == 0)  //weird
+            return E_FILE_FORMAT_INVALID;
+
+        //This is the distinguished set of ID's we use to determine
+        //that we have exhausted the sub-element's inside the cluster
+        //whose ID we parsed earlier.
+
+        if ((id == 0x0F43B675) || (id == 0x0C53BB6B)) //Cluster or Cues ID
+        {
+            if (m_element_size < 0)
+                m_element_size = pos - m_element_start;
+
+            break;
+        }
+
+        pos += len;  //consume ID field
+
+        //Parse Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;
+
+        pos += len;  //consume size field
+
+        if ((cluster_stop >= 0) && (pos > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        //pos now points to start of payload
+
+        if (size == 0)  //weird
+            continue;
+
+        //const long long block_start = pos;
+        const long long block_stop = pos + size;
+
+        if (cluster_stop >= 0)
+        {
+            if (block_stop > cluster_stop)
+            {
+                if ((id == 0x20) || (id == 0x23))
+                    return E_FILE_FORMAT_INVALID;
+
+                pos = cluster_stop;
+                break;
+            }
+        }
+        else if ((total >= 0) && (block_stop > total))
+        {
+            m_element_size = total - m_element_start;
+            pos = total;
+            break;
+        }
+        else if (block_stop > avail)
+        {
+            len = static_cast<long>(size);
+            return E_BUFFER_NOT_FULL;
+        }
+
+        Cluster* const this_ = const_cast<Cluster*>(this);
+
+        if (id == 0x20)  //BlockGroup
+            return this_->ParseBlockGroup(size, pos, len);
+
+        if (id == 0x23)  //SimpleBlock
+            return this_->ParseSimpleBlock(size, pos, len);
+
+        pos += size;  //consume payload
+        assert((cluster_stop < 0) || (pos <= cluster_stop));
+    }
+
+    assert(m_element_size > 0);
+
+    m_pos = pos;
+    assert((cluster_stop < 0) || (m_pos <= cluster_stop));
+
+    if (m_entries_count > 0)
+    {
+        const long idx = m_entries_count - 1;
+
+        const BlockEntry* const pLast = m_entries[idx];
+        assert(pLast);
+
+        const Block* const pBlock = pLast->GetBlock();
+        assert(pBlock);
+
+        const long long start = pBlock->m_start;
+
+        if ((total >= 0) && (start > total))
+            return -1;  //defend against trucated stream
+
+        const long long size = pBlock->m_size;
+
+        const long long stop = start + size;
+        assert((cluster_stop < 0) || (stop <= cluster_stop));
+
+        if ((total >= 0) && (stop > total))
+            return -1;  //defend against trucated stream
+    }
+
+    return 1;  //no more entries
+}
+
+
+long Cluster::ParseSimpleBlock(
+    long long block_size,
+    long long& pos,
+    long& len)
+{
+    const long long block_start = pos;
+    const long long block_stop = pos + block_size;
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long total, avail;
+
+    long status = pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    //parse track number
+
+    if ((pos + 1) > avail)
+    {
+        len = 1;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    long long result = GetUIntLength(pReader, pos, len);
+
+    if (result < 0)  //error
+        return static_cast<long>(result);
+
+    if (result > 0)  //weird
+        return E_BUFFER_NOT_FULL;
+
+    if ((pos + len) > block_stop)
+        return E_FILE_FORMAT_INVALID;
+
+    if ((pos + len) > avail)
+        return E_BUFFER_NOT_FULL;
+
+    const long long track = ReadUInt(pReader, pos, len);
+
+    if (track < 0) //error
+        return static_cast<long>(track);
+
+    if (track == 0)
+        return E_FILE_FORMAT_INVALID;
+
+#if 0
+    //TODO(matthewjheaney)
+    //This turned out to be too conservative.  The problem is that
+    //if we see a track header in the tracks element with an unsupported
+    //track type, we throw that track header away, so it is not present
+    //in the track map.  But even though we don't understand the track
+    //header, there are still blocks in the cluster with that track
+    //number.  It was our decision to ignore that track header, so it's
+    //up to us to deal with blocks associated with that track -- we
+    //cannot simply report an error since technically there's nothing
+    //wrong with the file.
+    //
+    //For now we go ahead and finish the parse, creating a block entry
+    //for this block.  This is somewhat wasteful, because without a
+    //track header there's nothing you can do with the block. What
+    //we really need here is a special return value that indicates to
+    //the caller that he should ignore this particular block, and
+    //continue parsing.
+
+    const Tracks* const pTracks = m_pSegment->GetTracks();
+    assert(pTracks);
+
+    const long tn = static_cast<long>(track);
+
+    const Track* const pTrack = pTracks->GetTrackByNumber(tn);
+
+    if (pTrack == NULL)
+        return E_FILE_FORMAT_INVALID;
+#endif
+
+    pos += len;  //consume track number
+
+    if ((pos + 2) > block_stop)
+        return E_FILE_FORMAT_INVALID;
+
+    if ((pos + 2) > avail)
+    {
+        len = 2;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    pos += 2;  //consume timecode
+
+    if ((pos + 1) > block_stop)
+        return E_FILE_FORMAT_INVALID;
+
+    if ((pos + 1) > avail)
+    {
+        len = 1;
+        return E_BUFFER_NOT_FULL;
+    }
+
+    unsigned char flags;
+
+    status = pReader->Read(pos, 1, &flags);
+
+    if (status < 0)  //error or underflow
+    {
+        len = 1;
+        return status;
+    }
+
+    ++pos;  //consume flags byte
+    assert(pos <= avail);
+
+    if (pos >= block_stop)
+        return E_FILE_FORMAT_INVALID;
+
+    const int lacing = int(flags & 0x06) >> 1;
+
+    if ((lacing != 0) && (block_stop > avail))
+    {
+        len = static_cast<long>(block_stop - pos);
+        return E_BUFFER_NOT_FULL;
+    }
+
+    status = CreateBlock(0x23,  //simple block id
+                         block_start, block_size,
+                         0);  //DiscardPadding
+
+    if (status != 0)
+        return status;
+
+    m_pos = block_stop;
+
+    return 0;  //success
+}
+
+
+long Cluster::ParseBlockGroup(
+    long long payload_size,
+    long long& pos,
+    long& len)
+{
+    const long long payload_start = pos;
+    const long long payload_stop = pos + payload_size;
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long total, avail;
+
+    long status = pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    if ((total >= 0) && (payload_stop > total))
+        return E_FILE_FORMAT_INVALID;
+
+    if (payload_stop > avail)
+    {
+         len = static_cast<long>(payload_size);
+         return E_BUFFER_NOT_FULL;
+    }
+
+    long long discard_padding = 0;
+
+    while (pos < payload_stop)
+    {
+        //parse sub-block element ID
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((pos + len) > payload_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id = ReadUInt(pReader, pos, len);
+
+        if (id < 0) //error
+            return static_cast<long>(id);
+
+        if (id == 0)  //not a value ID
+            return E_FILE_FORMAT_INVALID;
+
+        pos += len;  //consume ID field
+
+        //Parse Size
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((pos + len) > payload_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        pos += len;  //consume size field
+
+        //pos now points to start of sub-block group payload
+
+        if (pos > payload_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        if (size == 0)  //weird
+            continue;
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;
+
+        if (id == 0x35A2)  //DiscardPadding
+        {
+            result = GetUIntLength(pReader, pos, len);
+
+            if (result < 0)  //error
+                return static_cast<long>(result);
+
+            status = UnserializeInt(pReader, pos, len, discard_padding);
+
+            if (status < 0)  //error
+                return status;
+        }
+
+        if (id != 0x21)  //sub-part of BlockGroup is not a Block
+        {
+            pos += size;  //consume sub-part of block group
+
+            if (pos > payload_stop)
+                return E_FILE_FORMAT_INVALID;
+
+            continue;
+        }
+
+        const long long block_stop = pos + size;
+
+        if (block_stop > payload_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        //parse track number
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((pos + len) > block_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long track = ReadUInt(pReader, pos, len);
+
+        if (track < 0) //error
+            return static_cast<long>(track);
+
+        if (track == 0)
+            return E_FILE_FORMAT_INVALID;
+
+#if 0
+        //TODO(matthewjheaney)
+        //This turned out to be too conservative.  The problem is that
+        //if we see a track header in the tracks element with an unsupported
+        //track type, we throw that track header away, so it is not present
+        //in the track map.  But even though we don't understand the track
+        //header, there are still blocks in the cluster with that track
+        //number.  It was our decision to ignore that track header, so it's
+        //up to us to deal with blocks associated with that track -- we
+        //cannot simply report an error since technically there's nothing
+        //wrong with the file.
+        //
+        //For now we go ahead and finish the parse, creating a block entry
+        //for this block.  This is somewhat wasteful, because without a
+        //track header there's nothing you can do with the block. What
+        //we really need here is a special return value that indicates to
+        //the caller that he should ignore this particular block, and
+        //continue parsing.
+
+        const Tracks* const pTracks = m_pSegment->GetTracks();
+        assert(pTracks);
+
+        const long tn = static_cast<long>(track);
+
+        const Track* const pTrack = pTracks->GetTrackByNumber(tn);
+
+        if (pTrack == NULL)
+            return E_FILE_FORMAT_INVALID;
+#endif
+
+        pos += len;  //consume track number
+
+        if ((pos + 2) > block_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + 2) > avail)
+        {
+            len = 2;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        pos += 2;  //consume timecode
+
+        if ((pos + 1) > block_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        unsigned char flags;
+
+        status = pReader->Read(pos, 1, &flags);
+
+        if (status < 0)  //error or underflow
+        {
+            len = 1;
+            return status;
+        }
+
+        ++pos;  //consume flags byte
+        assert(pos <= avail);
+
+        if (pos >= block_stop)
+            return E_FILE_FORMAT_INVALID;
+
+        const int lacing = int(flags & 0x06) >> 1;
+
+        if ((lacing != 0) && (block_stop > avail))
+        {
+            len = static_cast<long>(block_stop - pos);
+            return E_BUFFER_NOT_FULL;
+        }
+
+        pos = block_stop;  //consume block-part of block group
+        assert(pos <= payload_stop);
+    }
+
+    assert(pos == payload_stop);
+
+    status = CreateBlock(0x20,  //BlockGroup ID
+                         payload_start, payload_size,
+                         discard_padding);
+    if (status != 0)
+        return status;
+
+    m_pos = payload_stop;
+
+    return 0;  //success
+}
+
+
+long Cluster::GetEntry(long index, const mkvparser::BlockEntry*& pEntry) const
+{
+    assert(m_pos >= m_element_start);
+
+    pEntry = NULL;
+
+    if (index < 0)
+        return -1;  //generic error
+
+    if (m_entries_count < 0)
+        return E_BUFFER_NOT_FULL;
+
+    assert(m_entries);
+    assert(m_entries_size > 0);
+    assert(m_entries_count <= m_entries_size);
+
+    if (index < m_entries_count)
+    {
+        pEntry = m_entries[index];
+        assert(pEntry);
+
+        return 1;  //found entry
+    }
+
+    if (m_element_size < 0)        //we don't know cluster end yet
+        return E_BUFFER_NOT_FULL;  //underflow
+
+    const long long element_stop = m_element_start + m_element_size;
+
+    if (m_pos >= element_stop)
+        return 0;  //nothing left to parse
+
+    return E_BUFFER_NOT_FULL;  //underflow, since more remains to be parsed
+}
+
+
+Cluster* Cluster::Create(
+    Segment* pSegment,
+    long idx,
+    long long off)
+    //long long element_size)
+{
+    assert(pSegment);
+    assert(off >= 0);
+
+    const long long element_start = pSegment->m_start + off;
+
+    Cluster* const pCluster = new Cluster(pSegment,
+                                          idx,
+                                          element_start);
+                                          //element_size);
+    assert(pCluster);
+
+    return pCluster;
+}
+
+
+Cluster::Cluster() :
+    m_pSegment(NULL),
+    m_element_start(0),
+    m_index(0),
+    m_pos(0),
+    m_element_size(0),
+    m_timecode(0),
+    m_entries(NULL),
+    m_entries_size(0),
+    m_entries_count(0)  //means "no entries"
+{
+}
+
+
+Cluster::Cluster(
+    Segment* pSegment,
+    long idx,
+    long long element_start
+    /* long long element_size */ ) :
+    m_pSegment(pSegment),
+    m_element_start(element_start),
+    m_index(idx),
+    m_pos(element_start),
+    m_element_size(-1 /* element_size */ ),
+    m_timecode(-1),
+    m_entries(NULL),
+    m_entries_size(0),
+    m_entries_count(-1)  //means "has not been parsed yet"
+{
+}
+
+
+Cluster::~Cluster()
+{
+    if (m_entries_count <= 0)
+        return;
+
+    BlockEntry** i = m_entries;
+    BlockEntry** const j = m_entries + m_entries_count;
+
+    while (i != j)
+    {
+         BlockEntry* p = *i++;
+         assert(p);
+
+         delete p;
+    }
+
+    delete[] m_entries;
+}
+
+
+bool Cluster::EOS() const
+{
+    return (m_pSegment == NULL);
+}
+
+
+long Cluster::GetIndex() const
+{
+    return m_index;
+}
+
+
+long long Cluster::GetPosition() const
+{
+    const long long pos = m_element_start - m_pSegment->m_start;
+    assert(pos >= 0);
+
+    return pos;
+}
+
+
+long long Cluster::GetElementSize() const
+{
+    return m_element_size;
+}
+
+
+#if 0
+bool Cluster::HasBlockEntries(
+    const Segment* pSegment,
+    long long off)  //relative to start of segment payload
+{
+    assert(pSegment);
+    assert(off >= 0);  //relative to segment
+
+    IMkvReader* const pReader = pSegment->m_pReader;
+
+    long long pos = pSegment->m_start + off;  //absolute
+    long long size;
+
+    {
+        long len;
+
+        const long long id = ReadUInt(pReader, pos, len);
+        (void)id;
+        assert(id >= 0);
+        assert(id == 0x0F43B675);  //Cluster ID
+
+        pos += len;  //consume id
+
+        size = ReadUInt(pReader, pos, len);
+        assert(size > 0);
+
+        pos += len;  //consume size
+
+        //pos now points to start of payload
+    }
+
+    const long long stop = pos + size;
+
+    while (pos < stop)
+    {
+        long len;
+
+        const long long id = ReadUInt(pReader, pos, len);
+        assert(id >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume id
+
+        const long long size = ReadUInt(pReader, pos, len);
+        assert(size >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume size
+
+        if (id == 0x20)  //BlockGroup ID
+            return true;
+
+        if (id == 0x23)  //SimpleBlock ID
+            return true;
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    return false;
+}
+#endif
+
+
+long Cluster::HasBlockEntries(
+    const Segment* pSegment,
+    long long off,  //relative to start of segment payload
+    long long& pos,
+    long& len)
+{
+    assert(pSegment);
+    assert(off >= 0);  //relative to segment
+
+    IMkvReader* const pReader = pSegment->m_pReader;
+
+    long long total, avail;
+
+    long status = pReader->Length(&total, &avail);
+
+    if (status < 0)  //error
+        return status;
+
+    assert((total < 0) || (avail <= total));
+
+    pos = pSegment->m_start + off;  //absolute
+
+    if ((total >= 0) && (pos >= total))
+        return 0;  //we don't even have a complete cluster
+
+    const long long segment_stop =
+        (pSegment->m_size < 0) ? -1 : pSegment->m_start + pSegment->m_size;
+
+    long long cluster_stop = -1;  //interpreted later to mean "unknown size"
+
+    {
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //need more data
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((total >= 0) && ((pos + len) > total))
+            return 0;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id = ReadUInt(pReader, pos, len);
+
+        if (id < 0)  //error
+            return static_cast<long>(id);
+
+        if (id != 0x0F43B675)  //weird: not cluster ID
+            return -1;         //generic error
+
+        pos += len;  //consume Cluster ID field
+
+        //read size field
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //weird
+            return E_BUFFER_NOT_FULL;
+
+        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((total >= 0) && ((pos + len) > total))
+            return 0;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        if (size == 0)
+            return 0;  //cluster does not have entries
+
+        pos += len;  //consume size field
+
+        //pos now points to start of payload
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size != unknown_size)
+        {
+            cluster_stop = pos + size;
+            assert(cluster_stop >= 0);
+
+            if ((segment_stop >= 0) && (cluster_stop > segment_stop))
+                return E_FILE_FORMAT_INVALID;
+
+            if ((total >= 0) && (cluster_stop > total))
+                //return E_FILE_FORMAT_INVALID;  //too conservative
+                return 0;  //cluster does not have any entries
+        }
+    }
+
+    for (;;)
+    {
+        if ((cluster_stop >= 0) && (pos >= cluster_stop))
+            return 0;  //no entries detected
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        long long result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //need more data
+            return E_BUFFER_NOT_FULL;
+
+        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long id = ReadUInt(pReader, pos, len);
+
+        if (id < 0)  //error
+            return static_cast<long>(id);
+
+        //This is the distinguished set of ID's we use to determine
+        //that we have exhausted the sub-element's inside the cluster
+        //whose ID we parsed earlier.
+
+        if (id == 0x0F43B675)  //Cluster ID
+            return 0;  //no entries found
+
+        if (id == 0x0C53BB6B)  //Cues ID
+            return 0;  //no entries found
+
+        pos += len;  //consume id field
+
+        if ((cluster_stop >= 0) && (pos >= cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        //read size field
+
+        if ((pos + 1) > avail)
+        {
+            len = 1;
+            return E_BUFFER_NOT_FULL;
+        }
+
+        result = GetUIntLength(pReader, pos, len);
+
+        if (result < 0)  //error
+            return static_cast<long>(result);
+
+        if (result > 0)  //underflow
+            return E_BUFFER_NOT_FULL;
+
+        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > avail)
+            return E_BUFFER_NOT_FULL;
+
+        const long long size = ReadUInt(pReader, pos, len);
+
+        if (size < 0)  //error
+            return static_cast<long>(size);
+
+        pos += len;  //consume size field
+
+        //pos now points to start of payload
+
+        if ((cluster_stop >= 0) && (pos > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if (size == 0)  //weird
+            continue;
+
+        const long long unknown_size = (1LL << (7 * len)) - 1;
+
+        if (size == unknown_size)
+            return E_FILE_FORMAT_INVALID;  //not supported inside cluster
+
+        if ((cluster_stop >= 0) && ((pos + size) > cluster_stop))
+            return E_FILE_FORMAT_INVALID;
+
+        if (id == 0x20)  //BlockGroup ID
+            return 1;    //have at least one entry
+
+        if (id == 0x23)  //SimpleBlock ID
+            return 1;    //have at least one entry
+
+        pos += size;  //consume payload
+        assert((cluster_stop < 0) || (pos <= cluster_stop));
+    }
+}
+
+
+long long Cluster::GetTimeCode() const
+{
+    long long pos;
+    long len;
+
+    const long status = Load(pos, len);
+
+    if (status < 0) //error
+        return status;
+
+    return m_timecode;
+}
+
+
+long long Cluster::GetTime() const
+{
+    const long long tc = GetTimeCode();
+
+    if (tc < 0)
+        return tc;
+
+    const SegmentInfo* const pInfo = m_pSegment->GetInfo();
+    assert(pInfo);
+
+    const long long scale = pInfo->GetTimeCodeScale();
+    assert(scale >= 1);
+
+    const long long t = m_timecode * scale;
+
+    return t;
+}
+
+
+long long Cluster::GetFirstTime() const
+{
+    const BlockEntry* pEntry;
+
+    const long status = GetFirst(pEntry);
+
+    if (status < 0)  //error
+        return status;
+
+    if (pEntry == NULL)  //empty cluster
+        return GetTime();
+
+    const Block* const pBlock = pEntry->GetBlock();
+    assert(pBlock);
+
+    return pBlock->GetTime(this);
+}
+
+
+long long Cluster::GetLastTime() const
+{
+    const BlockEntry* pEntry;
+
+    const long status = GetLast(pEntry);
+
+    if (status < 0)  //error
+        return status;
+
+    if (pEntry == NULL)  //empty cluster
+        return GetTime();
+
+    const Block* const pBlock = pEntry->GetBlock();
+    assert(pBlock);
+
+    return pBlock->GetTime(this);
+}
+
+
+long Cluster::CreateBlock(
+    long long id,
+    long long pos,   //absolute pos of payload
+    long long size,
+    long long discard_padding)
+{
+    assert((id == 0x20) || (id == 0x23));  //BlockGroup or SimpleBlock
+
+    if (m_entries_count < 0)  //haven't parsed anything yet
+    {
+        assert(m_entries == NULL);
+        assert(m_entries_size == 0);
+
+        m_entries_size = 1024;
+        m_entries = new BlockEntry*[m_entries_size];
+
+        m_entries_count = 0;
+    }
+    else
+    {
+        assert(m_entries);
+        assert(m_entries_size > 0);
+        assert(m_entries_count <= m_entries_size);
+
+        if (m_entries_count >= m_entries_size)
+        {
+            const long entries_size = 2 * m_entries_size;
+
+            BlockEntry** const entries = new BlockEntry*[entries_size];
+            assert(entries);
+
+            BlockEntry** src = m_entries;
+            BlockEntry** const src_end = src + m_entries_count;
+
+            BlockEntry** dst = entries;
+
+            while (src != src_end)
+                *dst++ = *src++;
+
+            delete[] m_entries;
+
+            m_entries = entries;
+            m_entries_size = entries_size;
+        }
+    }
+
+    if (id == 0x20)  //BlockGroup ID
+        return CreateBlockGroup(pos, size, discard_padding);
+    else  //SimpleBlock ID
+        return CreateSimpleBlock(pos, size);
+}
+
+
+long Cluster::CreateBlockGroup(
+    long long start_offset,
+    long long size,
+    long long discard_padding)
+{
+    assert(m_entries);
+    assert(m_entries_size > 0);
+    assert(m_entries_count >= 0);
+    assert(m_entries_count < m_entries_size);
+
+    IMkvReader* const pReader = m_pSegment->m_pReader;
+
+    long long pos = start_offset;
+    const long long stop = start_offset + size;
+
+    //For WebM files, there is a bias towards previous reference times
+    //(in order to support alt-ref frames, which refer back to the previous
+    //keyframe).  Normally a 0 value is not possible, but here we tenatively
+    //allow 0 as the value of a reference frame, with the interpretation
+    //that this is a "previous" reference time.
+
+    long long prev = 1;  //nonce
+    long long next = 0;  //nonce
+    long long duration = -1;  //really, this is unsigned
+
+    long long bpos = -1;
+    long long bsize = -1;
+
+    while (pos < stop)
+    {
+        long len;
+        const long long id = ReadUInt(pReader, pos, len);
+        assert(id >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume ID
+
+        const long long size = ReadUInt(pReader, pos, len);
+        assert(size >= 0);  //TODO
+        assert((pos + len) <= stop);
+
+        pos += len;  //consume size
+
+        if (id == 0x21) //Block ID
+        {
+            if (bpos < 0) //Block ID
+            {
+                bpos = pos;
+                bsize = size;
+            }
+        }
+        else if (id == 0x1B)  //Duration ID
+        {
+            assert(size <= 8);
+
+            duration = UnserializeUInt(pReader, pos, size);
+            assert(duration >= 0);  //TODO
+        }
+        else if (id == 0x7B)  //ReferenceBlock
+        {
+            assert(size <= 8);
+            const long size_ = static_cast<long>(size);
+
+            long long time;
+
+            long status = UnserializeInt(pReader, pos, size_, time);
+            assert(status == 0);
+            if (status != 0)
+                return -1;
+
+            if (time <= 0)  //see note above
+                prev = time;
+            else  //weird
+                next = time;
+        }
+
+        pos += size;  //consume payload
+        assert(pos <= stop);
+    }
+
+    assert(pos == stop);
+    assert(bpos >= 0);
+    assert(bsize >= 0);
+
+    const long idx = m_entries_count;
+
+    BlockEntry** const ppEntry = m_entries + idx;
+    BlockEntry*& pEntry = *ppEntry;
+
+    pEntry = new (std::nothrow) BlockGroup(
+                                  this,
+                                  idx,
+                                  bpos,
+                                  bsize,
+                                  prev,
+                                  next,
+                                  duration,
+                                  discard_padding);
+
+    if (pEntry == NULL)
+        return -1;  //generic error
+
+    BlockGroup* const p = static_cast<BlockGroup*>(pEntry);
+
+    const long status = p->Parse();
+
+    if (status == 0)  //success
+    {
+        ++m_entries_count;
+        return 0;
+    }
+
+    delete pEntry;
+    pEntry = 0;
+
+    return status;
+}
+
+
+
+long Cluster::CreateSimpleBlock(
+    long long st,
+    long long sz)
+{
+    assert(m_entries);
+    assert(m_entries_size > 0);
+    assert(m_entries_count >= 0);
+    assert(m_entries_count < m_entries_size);
+
+    const long idx = m_entries_count;
+
+    BlockEntry** const ppEntry = m_entries + idx;
+    BlockEntry*& pEntry = *ppEntry;
+
+    pEntry = new (std::nothrow) SimpleBlock(this, idx, st, sz);
+
+    if (pEntry == NULL)
+        return -1;  //generic error
+
+    SimpleBlock* const p = static_cast<SimpleBlock*>(pEntry);
+
+    const long status = p->Parse();
+
+    if (status == 0)
+    {
+        ++m_entries_count;
+        return 0;
+    }
+
+    delete pEntry;
+    pEntry = 0;
+
+    return status;
+}
+
+
+long Cluster::GetFirst(const BlockEntry*& pFirst) const
+{
+    if (m_entries_count <= 0)
+    {
+        long long pos;
+        long len;
+
+        const long status = Parse(pos, len);
+
+        if (status < 0)  //error
+        {
+            pFirst = NULL;
+            return status;
+        }
+
+        if (m_entries_count <= 0)  //empty cluster
+        {
+            pFirst = NULL;
+            return 0;
+        }
+    }
+
+    assert(m_entries);
+
+    pFirst = m_entries[0];
+    assert(pFirst);
+
+    return 0;  //success
+}
+
+long Cluster::GetLast(const BlockEntry*& pLast) const
+{
+    for (;;)
+    {
+        long long pos;
+        long len;
+
+        const long status = Parse(pos, len);
+
+        if (status < 0)  //error
+        {
+            pLast = NULL;
+            return status;
+        }
+
+        if (status > 0)  //no new block
+            break;
+    }
+
+    if (m_entries_count <= 0)
+    {
+        pLast = NULL;
+        return 0;
+    }
+
+    assert(m_entries);
+
+    const long idx = m_entries_count - 1;
+
+    pLast = m_entries[idx];
+    assert(pLast);
+
+    return 0;
+}
+
+
+long Cluster::GetNext(
+    const BlockEntry* pCurr,
+    const BlockEntry*& pNext) const
+{
+    assert(pCurr);
+    assert(m_entries);
+    assert(m_entries_count > 0);
+
+    size_t idx = pCurr->GetIndex();
+    assert(idx < size_t(m_entries_count));
+    assert(m_entries[idx] == pCurr);
+
+    ++idx;
+
+    if (idx >= size_t(m_entries_count))
+    {
+        long long pos;
+        long len;
+
+        const long status = Parse(pos, len);
+
+        if (status < 0)  //error
+        {
+            pNext = NULL;
+            return status;
+        }
+
+        if (status > 0)
+        {
+            pNext = NULL;
+            return 0;
+        }
+
+        assert(m_entries);
+        assert(m_entries_count > 0);
+        assert(idx < size_t(m_entries_count));
+    }
+
+    pNext = m_entries[idx];
+    assert(pNext);
+
+    return 0;
+}
+
+
+long Cluster::GetEntryCount() const
+{
+    return m_entries_count;
+}
+
+
+const BlockEntry* Cluster::GetEntry(
+    const Track* pTrack,
+    long long time_ns) const
+{
+    assert(pTrack);
+
+    if (m_pSegment == NULL)  //this is the special EOS cluster
+        return pTrack->GetEOS();
+
+#if 0
+
+    LoadBlockEntries();
+
+    if ((m_entries == NULL) || (m_entries_count <= 0))
+        return NULL;  //return EOS here?
+
+    const BlockEntry* pResult = pTrack->GetEOS();
+
+    BlockEntry** i = m_entries;
+    assert(i);
+
+    BlockEntry** const j = i + m_entries_count;
+
+    while (i != j)
+    {
+        const BlockEntry* const pEntry = *i++;
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if (pBlock->GetTrackNumber() != pTrack->GetNumber())
+            continue;
+
+        if (pTrack->VetEntry(pEntry))
+        {
+            if (time_ns < 0)  //just want first candidate block
+                return pEntry;
+
+            const long long ns = pBlock->GetTime(this);
+
+            if (ns > time_ns)
+                break;
+
+            pResult = pEntry;
+        }
+        else if (time_ns >= 0)
+        {
+            const long long ns = pBlock->GetTime(this);
+
+            if (ns > time_ns)
+                break;
+        }
+    }
+
+    return pResult;
+
+#else
+
+    const BlockEntry* pResult = pTrack->GetEOS();
+
+    long index = 0;
+
+    for (;;)
+    {
+        if (index >= m_entries_count)
+        {
+            long long pos;
+            long len;
+
+            const long status = Parse(pos, len);
+            assert(status >= 0);
+
+            if (status > 0)  //completely parsed, and no more entries
+                return pResult;
+
+            if (status < 0)  //should never happen
+                return 0;
+
+            assert(m_entries);
+            assert(index < m_entries_count);
+        }
+
+        const BlockEntry* const pEntry = m_entries[index];
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if (pBlock->GetTrackNumber() != pTrack->GetNumber())
+        {
+            ++index;
+            continue;
+        }
+
+        if (pTrack->VetEntry(pEntry))
+        {
+            if (time_ns < 0)  //just want first candidate block
+                return pEntry;
+
+            const long long ns = pBlock->GetTime(this);
+
+            if (ns > time_ns)
+                return pResult;
+
+            pResult = pEntry;  //have a candidate
+        }
+        else if (time_ns >= 0)
+        {
+            const long long ns = pBlock->GetTime(this);
+
+            if (ns > time_ns)
+                return pResult;
+        }
+
+        ++index;
+    }
+
+#endif
+}
+
+
+const BlockEntry*
+Cluster::GetEntry(
+    const CuePoint& cp,
+    const CuePoint::TrackPosition& tp) const
+{
+    assert(m_pSegment);
+
+#if 0
+
+    LoadBlockEntries();
+
+    if (m_entries == NULL)
+        return NULL;
+
+    const long long count = m_entries_count;
+
+    if (count <= 0)
+        return NULL;
+
+    const long long tc = cp.GetTimeCode();
+
+    if ((tp.m_block > 0) && (tp.m_block <= count))
+    {
+        const size_t block = static_cast<size_t>(tp.m_block);
+        const size_t index = block - 1;
+
+        const BlockEntry* const pEntry = m_entries[index];
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if ((pBlock->GetTrackNumber() == tp.m_track) &&
+            (pBlock->GetTimeCode(this) == tc))
+        {
+            return pEntry;
+        }
+    }
+
+    const BlockEntry* const* i = m_entries;
+    const BlockEntry* const* const j = i + count;
+
+    while (i != j)
+    {
+#ifdef _DEBUG
+        const ptrdiff_t idx = i - m_entries;
+        idx;
+#endif
+
+        const BlockEntry* const pEntry = *i++;
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if (pBlock->GetTrackNumber() != tp.m_track)
+            continue;
+
+        const long long tc_ = pBlock->GetTimeCode(this);
+        assert(tc_ >= 0);
+
+        if (tc_ < tc)
+            continue;
+
+        if (tc_ > tc)
+            return NULL;
+
+        const Tracks* const pTracks = m_pSegment->GetTracks();
+        assert(pTracks);
+
+        const long tn = static_cast<long>(tp.m_track);
+        const Track* const pTrack = pTracks->GetTrackByNumber(tn);
+
+        if (pTrack == NULL)
+            return NULL;
+
+        const long long type = pTrack->GetType();
+
+        if (type == 2)  //audio
+            return pEntry;
+
+        if (type != 1)  //not video
+            return NULL;
+
+        if (!pBlock->IsKey())
+            return NULL;
+
+        return pEntry;
+    }
+
+    return NULL;
+
+#else
+
+    const long long tc = cp.GetTimeCode();
+
+    if (tp.m_block > 0)
+    {
+        const long block = static_cast<long>(tp.m_block);
+        const long index = block - 1;
+
+        while (index >= m_entries_count)
+        {
+            long long pos;
+            long len;
+
+            const long status = Parse(pos, len);
+
+            if (status < 0)  //TODO: can this happen?
+                return NULL;
+
+            if (status > 0)  //nothing remains to be parsed
+                return NULL;
+        }
+
+        const BlockEntry* const pEntry = m_entries[index];
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if ((pBlock->GetTrackNumber() == tp.m_track) &&
+            (pBlock->GetTimeCode(this) == tc))
+        {
+            return pEntry;
+        }
+    }
+
+    long index = 0;
+
+    for (;;)
+    {
+        if (index >= m_entries_count)
+        {
+            long long pos;
+            long len;
+
+            const long status = Parse(pos, len);
+
+            if (status < 0)  //TODO: can this happen?
+                return NULL;
+
+            if (status > 0)  //nothing remains to be parsed
+                return NULL;
+
+            assert(m_entries);
+            assert(index < m_entries_count);
+        }
+
+        const BlockEntry* const pEntry = m_entries[index];
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if (pBlock->GetTrackNumber() != tp.m_track)
+        {
+            ++index;
+            continue;
+        }
+
+        const long long tc_ = pBlock->GetTimeCode(this);
+
+        if (tc_ < tc)
+        {
+            ++index;
+            continue;
+        }
+
+        if (tc_ > tc)
+            return NULL;
+
+        const Tracks* const pTracks = m_pSegment->GetTracks();
+        assert(pTracks);
+
+        const long tn = static_cast<long>(tp.m_track);
+        const Track* const pTrack = pTracks->GetTrackByNumber(tn);
+
+        if (pTrack == NULL)
+            return NULL;
+
+        const long long type = pTrack->GetType();
+
+        if (type == 2)  //audio
+            return pEntry;
+
+        if (type != 1)  //not video
+            return NULL;
+
+        if (!pBlock->IsKey())
+            return NULL;
+
+        return pEntry;
+    }
+
+#endif
+
+}
+
+
+#if 0
+const BlockEntry* Cluster::GetMaxKey(const VideoTrack* pTrack) const
+{
+    assert(pTrack);
+
+    if (m_pSegment == NULL)  //EOS
+        return pTrack->GetEOS();
+
+    LoadBlockEntries();
+
+    if ((m_entries == NULL) || (m_entries_count <= 0))
+        return pTrack->GetEOS();
+
+    BlockEntry** i = m_entries + m_entries_count;
+    BlockEntry** const j = m_entries;
+
+    while (i != j)
+    {
+        const BlockEntry* const pEntry = *--i;
+        assert(pEntry);
+        assert(!pEntry->EOS());
+
+        const Block* const pBlock = pEntry->GetBlock();
+        assert(pBlock);
+
+        if (pBlock->GetTrackNumber() != pTrack->GetNumber())
+            continue;
+
+        if (pBlock->IsKey())
+            return pEntry;
+    }
+
+    return pTrack->GetEOS();  //no satisfactory block found
+}
+#endif
+
+
+BlockEntry::BlockEntry(Cluster* p, long idx) :
+    m_pCluster(p),
+    m_index(idx)
+{
+}
+
+
+BlockEntry::~BlockEntry()
+{
+}
+
+
+bool BlockEntry::EOS() const
+{
+    return (GetKind() == kBlockEOS);
+}
+
+
+const Cluster* BlockEntry::GetCluster() const
+{
+    return m_pCluster;
+}
+
+
+long BlockEntry::GetIndex() const
+{
+    return m_index;
+}
+
+
+SimpleBlock::SimpleBlock(
+    Cluster* pCluster,
+    long idx,
+    long long start,
+    long long size) :
+    BlockEntry(pCluster, idx),
+    m_block(start, size, 0)
+{
+}
+
+
+long SimpleBlock::Parse()
+{
+    return m_block.Parse(m_pCluster);
+}
+
+
+BlockEntry::Kind SimpleBlock::GetKind() const
+{
+    return kBlockSimple;
+}
+
+
+const Block* SimpleBlock::GetBlock() const
+{
+    return &m_block;
+}
+
+
+BlockGroup::BlockGroup(
+    Cluster* pCluster,
+    long idx,
+    long long block_start,
+    long long block_size,
+    long long prev,
+    long long next,
+    long long duration,
+    long long discard_padding) :
+    BlockEntry(pCluster, idx),
+    m_block(block_start, block_size, discard_padding),
+    m_prev(prev),
+    m_next(next),
+    m_duration(duration)
+{
+}
+
+
+long BlockGroup::Parse()
+{
+    const long status = m_block.Parse(m_pCluster);
+
+    if (status)
+        return status;
+
+    m_block.SetKey((m_prev > 0) && (m_next <= 0));
+
+    return 0;
+}
+
+
+#if 0
+void BlockGroup::ParseBlock(long long start, long long size)
+{
+    IMkvReader* const pReader = m_pCluster->m_pSegment->m_pReader;
+
+    Block* const pBlock = new Block(start, size, pReader);
+    assert(pBlock);  //TODO
+
+    //TODO: the Matroska spec says you have multiple blocks within the
+    //same block group, with blocks ranked by priority (the flag bits).
+
+    assert(m_pBlock == NULL);
+    m_pBlock = pBlock;
+}
+#endif
+
+
+BlockEntry::Kind BlockGroup::GetKind() const
+{
+    return kBlockGroup;
+}
+
+
+const Block* BlockGroup::GetBlock() const
+{
+    return &m_block;
+}
+
+
+long long BlockGroup::GetPrevTimeCode() const
+{
+    return m_prev;
+}
+
+
+long long BlockGroup::GetNextTimeCode() const
+{
+    return m_next;
+}
+
+long long BlockGroup::GetDurationTimeCode() const
+{
+    return m_duration;
+}
+
+Block::Block(long long start, long long size_, long long discard_padding) :
+    m_start(start),
+    m_size(size_),
+    m_track(0),
+    m_timecode(-1),
+    m_flags(0),
+    m_frames(NULL),
+    m_frame_count(-1),
+    m_discard_padding(discard_padding)
+{
+}
+
+
+Block::~Block()
+{
+    delete[] m_frames;
+}
+
+
+long Block::Parse(const Cluster* pCluster)
+{
+    if (pCluster == NULL)
+        return -1;
+
+    if (pCluster->m_pSegment == NULL)
+        return -1;
+
+    assert(m_start >= 0);
+    assert(m_size >= 0);
+    assert(m_track <= 0);
+    assert(m_frames == NULL);
+    assert(m_frame_count <= 0);
+
+    long long pos = m_start;
+    const long long stop = m_start + m_size;
+
+    long len;
+
+    IMkvReader* const pReader = pCluster->m_pSegment->m_pReader;
+
+    m_track = ReadUInt(pReader, pos, len);
+
+    if (m_track <= 0)
+        return E_FILE_FORMAT_INVALID;
+
+    if ((pos + len) > stop)
+        return E_FILE_FORMAT_INVALID;
+
+    pos += len;  //consume track number
+
+    if ((stop - pos) < 2)
+        return E_FILE_FORMAT_INVALID;
+
+    long status;
+    long long value;
+
+    status = UnserializeInt(pReader, pos, 2, value);
+
+    if (status)
+        return E_FILE_FORMAT_INVALID;
+
+    if (value < SHRT_MIN)
+        return E_FILE_FORMAT_INVALID;
+
+    if (value > SHRT_MAX)
+        return E_FILE_FORMAT_INVALID;
+
+    m_timecode = static_cast<short>(value);
+
+    pos += 2;
+
+    if ((stop - pos) <= 0)
+        return E_FILE_FORMAT_INVALID;
+
+    status = pReader->Read(pos, 1, &m_flags);
+
+    if (status)
+        return E_FILE_FORMAT_INVALID;
+
+    const int lacing = int(m_flags & 0x06) >> 1;
+
+    ++pos;  //consume flags byte
+
+    if (lacing == 0)  //no lacing
+    {
+        if (pos > stop)
+            return E_FILE_FORMAT_INVALID;
+
+        m_frame_count = 1;
+        m_frames = new Frame[m_frame_count];
+
+        Frame& f = m_frames[0];
+        f.pos = pos;
+
+        const long long frame_size = stop - pos;
+
+        if (frame_size > LONG_MAX)
+            return E_FILE_FORMAT_INVALID;
+
+        f.len = static_cast<long>(frame_size);
+
+        return 0;  //success
+    }
+
+    if (pos >= stop)
+        return E_FILE_FORMAT_INVALID;
+
+    unsigned char biased_count;
+
+    status = pReader->Read(pos, 1, &biased_count);
+
+    if (status)
+        return E_FILE_FORMAT_INVALID;
+
+    ++pos;  //consume frame count
+    assert(pos <= stop);
+
+    m_frame_count = int(biased_count) + 1;
+
+    m_frames = new Frame[m_frame_count];
+    assert(m_frames);
+
+    if (lacing == 1)  //Xiph
+    {
+        Frame* pf = m_frames;
+        Frame* const pf_end = pf + m_frame_count;
+
+        long size = 0;
+        int frame_count = m_frame_count;
+
+        while (frame_count > 1)
+        {
+            long frame_size = 0;
+
+            for (;;)
+            {
+                unsigned char val;
+
+                if (pos >= stop)
+                    return E_FILE_FORMAT_INVALID;
+
+                status = pReader->Read(pos, 1, &val);
+
+                if (status)
+                    return E_FILE_FORMAT_INVALID;
+
+                ++pos;  //consume xiph size byte
+
+                frame_size += val;
+
+                if (val < 255)
+                    break;
+            }
+
+            Frame& f = *pf++;
+            assert(pf < pf_end);
+
+            f.pos = 0;  //patch later
+
+            f.len = frame_size;
+            size += frame_size;  //contribution of this frame
+
+            --frame_count;
+        }
+
+        assert(pf < pf_end);
+        assert(pos <= stop);
+
+        {
+            Frame& f = *pf++;
+
+            if (pf != pf_end)
+                return E_FILE_FORMAT_INVALID;
+
+            f.pos = 0;  //patch later
+
+            const long long total_size = stop - pos;
+
+            if (total_size < size)
+                return E_FILE_FORMAT_INVALID;
+
+            const long long frame_size = total_size - size;
+
+            if (frame_size > LONG_MAX)
+                return E_FILE_FORMAT_INVALID;
+
+            f.len = static_cast<long>(frame_size);
+        }
+
+        pf = m_frames;
+        while (pf != pf_end)
+        {
+            Frame& f = *pf++;
+            assert((pos + f.len) <= stop);
+
+            f.pos = pos;
+            pos += f.len;
+        }
+
+        assert(pos == stop);
+    }
+    else if (lacing == 2)  //fixed-size lacing
+    {
+        const long long total_size = stop - pos;
+
+        if ((total_size % m_frame_count) != 0)
+            return E_FILE_FORMAT_INVALID;
+
+        const long long frame_size = total_size / m_frame_count;
+
+        if (frame_size > LONG_MAX)
+            return E_FILE_FORMAT_INVALID;
+
+        Frame* pf = m_frames;
+        Frame* const pf_end = pf + m_frame_count;
+
+        while (pf != pf_end)
+        {
+            assert((pos + frame_size) <= stop);
+
+            Frame& f = *pf++;
+
+            f.pos = pos;
+            f.len = static_cast<long>(frame_size);
+
+            pos += frame_size;
+        }
+
+        assert(pos == stop);
+    }
+    else
+    {
+        assert(lacing == 3);  //EBML lacing
+
+        if (pos >= stop)
+            return E_FILE_FORMAT_INVALID;
+
+        long size = 0;
+        int frame_count = m_frame_count;
+
+        long long frame_size = ReadUInt(pReader, pos, len);
+
+        if (frame_size < 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (frame_size > LONG_MAX)
+            return E_FILE_FORMAT_INVALID;
+
+        if ((pos + len) > stop)
+            return E_FILE_FORMAT_INVALID;
+
+        pos += len; //consume length of size of first frame
+
+        if ((pos + frame_size) > stop)
+            return E_FILE_FORMAT_INVALID;
+
+        Frame* pf = m_frames;
+        Frame* const pf_end = pf + m_frame_count;
+
+        {
+            Frame& curr = *pf;
+
+            curr.pos = 0;  //patch later
+
+            curr.len = static_cast<long>(frame_size);
+            size += curr.len;  //contribution of this frame
+        }
+
+        --frame_count;
+
+        while (frame_count > 1)
+        {
+            if (pos >= stop)
+                return E_FILE_FORMAT_INVALID;
+
+            assert(pf < pf_end);
+
+            const Frame& prev = *pf++;
+            assert(prev.len == frame_size);
+            if (prev.len != frame_size)
+                return E_FILE_FORMAT_INVALID;
+
+            assert(pf < pf_end);
+
+            Frame& curr = *pf;
+
+            curr.pos = 0;  //patch later
+
+            const long long delta_size_ = ReadUInt(pReader, pos, len);
+
+            if (delta_size_ < 0)
+                return E_FILE_FORMAT_INVALID;
+
+            if ((pos + len) > stop)
+                return E_FILE_FORMAT_INVALID;
+
+            pos += len;  //consume length of (delta) size
+            assert(pos <= stop);
+
+            const int exp = 7*len - 1;
+            const long long bias = (1LL << exp) - 1LL;
+            const long long delta_size = delta_size_ - bias;
+
+            frame_size += delta_size;
+
+            if (frame_size < 0)
+                return E_FILE_FORMAT_INVALID;
+
+            if (frame_size > LONG_MAX)
+                return E_FILE_FORMAT_INVALID;
+
+            curr.len = static_cast<long>(frame_size);
+            size += curr.len;  //contribution of this frame
+
+            --frame_count;
+        }
+
+        {
+            assert(pos <= stop);
+            assert(pf < pf_end);
+
+            const Frame& prev = *pf++;
+            assert(prev.len == frame_size);
+            if (prev.len != frame_size)
+                return E_FILE_FORMAT_INVALID;
+
+            assert(pf < pf_end);
+
+            Frame& curr = *pf++;
+            assert(pf == pf_end);
+
+            curr.pos = 0;  //patch later
+
+            const long long total_size = stop - pos;
+
+            if (total_size < size)
+                return E_FILE_FORMAT_INVALID;
+
+            frame_size = total_size - size;
+
+            if (frame_size > LONG_MAX)
+                return E_FILE_FORMAT_INVALID;
+
+            curr.len = static_cast<long>(frame_size);
+        }
+
+        pf = m_frames;
+        while (pf != pf_end)
+        {
+            Frame& f = *pf++;
+            assert((pos + f.len) <= stop);
+
+            f.pos = pos;
+            pos += f.len;
+        }
+
+        assert(pos == stop);
+    }
+
+    return 0;  //success
+}
+
+
+long long Block::GetTimeCode(const Cluster* pCluster) const
+{
+    if (pCluster == 0)
+        return m_timecode;
+
+    const long long tc0 = pCluster->GetTimeCode();
+    assert(tc0 >= 0);
+
+    const long long tc = tc0 + m_timecode;
+
+    return tc;  //unscaled timecode units
+}
+
+
+long long Block::GetTime(const Cluster* pCluster) const
+{
+    assert(pCluster);
+
+    const long long tc = GetTimeCode(pCluster);
+
+    const Segment* const pSegment = pCluster->m_pSegment;
+    const SegmentInfo* const pInfo = pSegment->GetInfo();
+    assert(pInfo);
+
+    const long long scale = pInfo->GetTimeCodeScale();
+    assert(scale >= 1);
+
+    const long long ns = tc * scale;
+
+    return ns;
+}
+
+
+long long Block::GetTrackNumber() const
+{
+    return m_track;
+}
+
+
+bool Block::IsKey() const
+{
+    return ((m_flags & static_cast<unsigned char>(1 << 7)) != 0);
+}
+
+
+void Block::SetKey(bool bKey)
+{
+    if (bKey)
+        m_flags |= static_cast<unsigned char>(1 << 7);
+    else
+        m_flags &= 0x7F;
+}
+
+
+bool Block::IsInvisible() const
+{
+    return bool(int(m_flags & 0x08) != 0);
+}
+
+
+Block::Lacing Block::GetLacing() const
+{
+    const int value = int(m_flags & 0x06) >> 1;
+    return static_cast<Lacing>(value);
+}
+
+
+int Block::GetFrameCount() const
+{
+    return m_frame_count;
+}
+
+
+const Block::Frame& Block::GetFrame(int idx) const
+{
+    assert(idx >= 0);
+    assert(idx < m_frame_count);
+
+    const Frame& f = m_frames[idx];
+    assert(f.pos > 0);
+    assert(f.len > 0);
+
+    return f;
+}
+
+
+long Block::Frame::Read(IMkvReader* pReader, unsigned char* buf) const
+{
+    assert(pReader);
+    assert(buf);
+
+    const long status = pReader->Read(pos, len, buf);
+    return status;
+}
+
+long long Block::GetDiscardPadding() const
+{
+    return m_discard_padding;
+}
+
+}  //end namespace mkvparser