Implement reading of media track info from WebM and MP4 containers

media/formats/mp4/box_definitions.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/formats/mp4/box_definitions.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 357 matching lines @@
 bool Edit::Parse(BoxReader* reader) {
   return reader->ScanChildren() && reader->ReadChild(&list);
 }
 
 HandlerReference::HandlerReference() : type(kInvalid) {}
 HandlerReference::~HandlerReference() {}
 FourCC HandlerReference::BoxType() const { return FOURCC_HDLR; }
 
 bool HandlerReference::Parse(BoxReader* reader) {
   FourCC hdlr_type;
-  RCHECK(reader->SkipBytes(8) && reader->ReadFourCC(&hdlr_type));
-  // Note: remaining fields in box ignored
+  RCHECK(reader->ReadFullBoxHeader() && reader->SkipBytes(4) &&
+         reader->ReadFourCC(&hdlr_type) && reader->SkipBytes(12));
+
+  // Now we should be at the beginning of the |name| field of HDLR box. The
+  // |name| is a zero-terminated ASCII string in ISO BMFF, but it was a
+  // Pascal-style counted string in older QT/Mov formats. So we'll read the
+  // remaining box bytes first, then if the last one is zero, we strip the last
+  // zero byte, otherwise we'll string the first byte (containing the length of
+  // the Pascal-style string).
+  std::vector<uint8_t> name_bytes;
+  RCHECK(reader->ReadVec(&name_bytes, reader->size() - reader->pos()));
+  if (name_bytes.back() == 0) {
+    name_bytes.pop_back();
+  } else {
+    // Check that the length of the Pascal-style string is correct.
+    RCHECK(name_bytes[0] == (name_bytes.size() - 1));

[wolenetz, 2016/03/10 19:53:29]

Is it possible that a 0-byte name_bytes might occur legally and let us reach
l.389 in this patch set? If so, please condition this whole block (l.389-l.395)
on actually having some name_bytes; otherwise we risk out-of-range access.

[servolk, 2016/03/10 22:25:38]

Done.

+    name_bytes.erase(name_bytes.begin());
+  }
+  name = std::string(name_bytes.begin(), name_bytes.end());
+
   if (hdlr_type == FOURCC_VIDE) {
     type = kVideo;
   } else if (hdlr_type == FOURCC_SOUN) {
     type = kAudio;
   } else {
     type = kInvalid;
   }
   return true;
 }
 
@@ skipping 235 matching lines @@
 
   // ESDS is not valid in case of EAC3.
   RCHECK(reader->MaybeReadChild(&esds));
   return true;
 }
 
 MediaHeader::MediaHeader()
     : creation_time(0),
       modification_time(0),
       timescale(0),
-      duration(0) {}
+      duration(0),
+      language_code(0) {}
 MediaHeader::~MediaHeader() {}
 FourCC MediaHeader::BoxType() const { return FOURCC_MDHD; }
 
 bool MediaHeader::Parse(BoxReader* reader) {

[wolenetz, 2016/03/10 19:53:29]

aside: please reference potential for mp4 ELNG to have better/different info in
the requested-to-be-filed crbug around figuring out if the specs are being sane
w.r.t. sourcing and exposing track language attribute.

[servolk, 2016/03/10 22:25:38]

Done: crbug.com/593904

   RCHECK(reader->ReadFullBoxHeader());
 
   if (reader->version() == 1) {
-    RCHECK(reader->Read8(&creation_time) &&
-           reader->Read8(&modification_time) &&
-           reader->Read4(&timescale) &&
-           reader->Read8(&duration));
+    RCHECK(reader->Read8(&creation_time) && reader->Read8(&modification_time) &&
+           reader->Read4(&timescale) && reader->Read8(&duration) &&
+           reader->Read2(&language_code));
   } else {
     RCHECK(reader->Read4Into8(&creation_time) &&
            reader->Read4Into8(&modification_time) &&
-           reader->Read4(&timescale) &&
-           reader->Read4Into8(&duration));
+           reader->Read4(&timescale) && reader->Read4Into8(&duration) &&
+           reader->Read2(&language_code));
   }
-  // Skip language information
-  return reader->SkipBytes(4);
+  // ISO 639-2/T language code only uses 15 lower bits, so reset the 16th bit.
+  language_code &= 0x7fff;
+  // Skip playback quality information
+  return reader->SkipBytes(2);
+}
+
+std::string MediaHeader::language() const {
+  if (language_code == 0x7fff || language_code < 0x400) {
+    return "und";
+  }
+  char lang_chars[4];
+  lang_chars[3] = 0;
+  lang_chars[2] = 0x60 + (language_code & 0x1f);
+  lang_chars[1] = 0x60 + ((language_code >> 5) & 0x1f);
+  lang_chars[0] = 0x60 + ((language_code >> 10) & 0x1f);
+
+  if (lang_chars[0] < 'a' || lang_chars[0] > 'z' || lang_chars[1] < 'a' ||
+      lang_chars[1] > 'z' || lang_chars[2] < 'a' || lang_chars[2] > 'z') {
+    // Got unexpected characteds in ISO 639-2/T language code. Something must be
+    // wrong with the input file, report 'und' language to be safe.
+    DVLOG(2) << "Ignoring MDHD language_code (non ISO 639-2 compliant): "
+             << lang_chars;
+    lang_chars[0] = 'u';
+    lang_chars[1] = 'n';
+    lang_chars[2] = 'd';
+  }
+
+  return lang_chars;
 }
 
 MediaInformation::MediaInformation() {}
 MediaInformation::~MediaInformation() {}
 FourCC MediaInformation::BoxType() const { return FOURCC_MINF; }
 
 bool MediaInformation::Parse(BoxReader* reader) {
   return reader->ScanChildren() &&
          reader->ReadChild(&sample_table);
 }
@@ skipping 376 matching lines @@
 SampleDependsOn IndependentAndDisposableSamples::sample_depends_on(
     size_t i) const {
   if (i >= sample_depends_on_.size())
     return kSampleDependsOnUnknown;
 
   return sample_depends_on_[i];
 }
 
 }  // namespace mp4
 }  // namespace media