Add UMA stats for audio/video containers.

media/base/container_names.cc

+// Copyright (c) 2013 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/base/container_names.h"
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/metrics/sparse_histogram.h"
+
+namespace media {
+
+#define TAG(a, b, c, d) \
+  ((static_cast<uint8_t>(a) << 24) | (static_cast<uint8_t>(b) << 16) | \
+   (static_cast<uint8_t>(c) << 8) | (static_cast<uint8_t>(d)))
+
+// Helper function to read 2 bytes (16 bits, big endian) from a buffer.
+static uint32_t Read16(const uint8_t* p) {
+  return p[0] << 8 | p[1];
+}
+
+// Helper function to read 3 bytes (24 bits, big endian) from a buffer.
+static uint32_t Read24(const uint8_t* p) {
+  return p[0] << 16 | p[1] << 8 | p[2];
+}
+
+// Helper function to read 4 bytes (32 bits, big endian) from a buffer.
+static uint32_t Read32(const uint8_t* p) {
+  return p[0] << 24 | p[1] << 16 | p[2] << 8 | p[3];
+}
+
+// Helper function to do buffer comparisons without going off the end
+// of the buffer.
+static bool CompareEqual(const uint8_t* buffer,

[xhwang, 2013/05/03 19:59:06]

This function is checking that "search" is a prefix of "buffer", not checking
they are equal. Rename as such?

[jrummell, 2013/05/03 23:56:21]

Done.

+                         size_t buffer_size,
+                         const char* search,
+                         size_t search_size) {
+  return (search_size <= buffer_size &&
+          memcmp(buffer, search, search_size) == 0);
+}
+
+// Comparison function used by lower_bound which returns true
+// if the first argument is less than the second.

[xhwang, 2013/05/03 19:59:06]

s/less than the second/less than the second in lexicographical order/

[jrummell, 2013/05/03 23:56:21]

Done.

+static bool ContainerNameMappingComparer(const ContainerNameMapping& a,
+                                         const char* b) {
+  return strcasecmp(a.name, b) < 0;
+}
+
+// Output a container value to the histogram.
+static void LogContainerToHistogram(FFmpegContainerName container,
+                                    bool is_guess) {
+  int metric = 2 * container;
+  if (is_guess)
+    ++metric;
+
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Media.DetectedContainer", metric);
+}
+
+// For some formats the signature is a bunch of characters. They are defined
+// below. Note that the first 4 characters of the string may be used as a TAG
+// in LookupContainerByFirst4.
+#define BYTE_ORDER_MARK      "\xef\xbb\xbf"
+
+static const char kAmrSignature[] = "#!AMR";
+static const char kApcSignature[] = "CRYO_APC";
+static const char kAsfSignature[] =
+    "\x30\x26\xb2\x75\x8e\x66\xcf\x11\xa6\xd9\x00\xaa\x00\x62\xce\x6c";
+static const char kAssSignature[] = "[Script Info]";
+static const char kAssBomSignature[] = BYTE_ORDER_MARK "[Script Info]";
+static const char kConcatSignature[] = "ffconcat version 1.0";
+static const char kDnxhdSignature[] = "\x00\x00\x02\x80\x01";
+static const char kFfSignature[] = ";FFMETADATA";
+static const char kHlsSignature[] = "#EXTM3U";
+static const char kIdfSignature[] =
+    "\x04\x31\x2e\x34\x00\x00\x00\x00\x4f\x00\x15\x00";
+static const char kIlbcSignature[] = "#!iLBC";
+static const char kIssSignature[] = "IMA_ADPCM_Sound";
+static const char kIv8Signature[] = "\x01\x01\x03\xb8\x80\x60";
+static const char kJvSignature[] = " Compression by John M Phillips Copyright "
+                                   "(C) 1995 The Bitmap Brothers Ltd.";
+static const char kLibnutSignature[] = "nut/multimedia container";
+static const char kLxfSignature[] = "LEITCH\x00\x00";
+static const char kNuv1Signature[] = "NuppelVideo";
+static const char kNuv2Signature[] = "MythTVVideo";
+static const char kPafSignature[] =
+    "Packed Animation File V1.0\n(c) 1992-96 Amazing Studio\x0a\x1a";
+static const char kRealSignature[] = "<window";
+static const char kRealBomSignature[] = BYTE_ORDER_MARK "<window";
+static const char kRplSignature[] = "ARMovie\x0A";
+static const char kSamiSignature[] = "<SAMI>";
+static const char kSamiBomSignature[] = BYTE_ORDER_MARK "<SAMI>";
+static const char kSmjpegSignature[] = "\x00\x0aSMJPEG";
+static const char kVivoSignature[] = "\r\nVersion:Vivo/";
+static const char kVobsubSignature[] = "# VobSub index file,";
+static const char kVocSignature[] = "Creative Voice File\x1A";
+static const char kW64Signature[] =
+    "riff\x2e\x91\xcf\x11\xa5\xd6\x28\xdb\x04\xc1\x00\x00";
+static const char kW64Signature2[] =
+    "wave\xf3\xac\xd3\x11\x8c\xd1\x00\xc0\x4f\x8e\xdb\x8a";
+static const char kWebvttSignature[] = "WEBVTT";
+static const char kWebvttBomSignature[] = BYTE_ORDER_MARK "WEBVTT";
+static const char kWtvSignature[] =
+    "\xb7\xd8\x00\x20\x37\x49\xda\x11\xa6\x4e\x00\x07\xe9\x5e\xad\x8d";
+static const char kYuv4Signature[] = "YUV4MPEG2";
+
+const uint16_t ac3_frame_size_table[38][3] = {

[xhwang, 2013/05/03 19:59:06]

use kCamelCase for consts?

[jrummell, 2013/05/03 23:56:21]

Done.

+  { 128, 138, 192 }, { 128, 140, 192 }, { 160, 174, 240 }, { 160, 176, 240 },
+  { 192, 208, 288 }, { 192, 210, 288 }, { 224, 242, 336 }, { 224, 244, 336 },
+  { 256, 278, 384 }, { 256, 280, 384 }, { 320, 348, 480 }, { 320, 350, 480 },
+  { 384, 416, 576 }, { 384, 418, 576 }, { 448, 486, 672 }, { 448, 488, 672 },
+  { 512, 556, 768 }, { 512, 558, 768 }, { 640, 696, 960 }, { 640, 698, 960 },
+  { 768, 834, 1152 }, { 768, 836, 1152 }, { 896, 974, 1344 },
+  { 896, 976, 1344 }, { 1024, 1114, 1536 }, { 1024, 1116, 1536 },
+  { 1280, 1392, 1920 }, { 1280, 1394, 1920 }, { 1536, 1670, 2304 },
+  { 1536, 1672, 2304 }, { 1792, 1950, 2688 }, { 1792, 1952, 2688 },
+  { 2048, 2228, 3072 }, { 2048, 2230, 3072 }, { 2304, 2506, 3456 },
+  { 2304, 2508, 3456 }, { 2560, 2768, 3840 }, { 2560, 2770, 3840 },
+};
+
+// Checks for an ADTS AAC container.
+static bool check_aac(const uint8_t buffer[], size_t buffer_size) {

[xhwang, 2013/05/03 19:59:06]

use const uint8_t* and int?

[jrummell, 2013/05/03 23:56:21]

Done.

+  // ADTS header is 7 or 9 bytes
+  // (from http://wiki.multimedia.cx/index.php?title=ADTS)
+  size_t offset = 0;
+  while (offset + 5 < buffer_size) {
+    uint32_t syncword = (Read16(buffer + offset) >> 4) & 0xfff;

[xhwang, 2013/05/03 19:59:06]

we are using uint32_t in this function even for 16bit integer. Then we are also
using "int" for the result of bitwise operations (e.g. on line 147). Are these
all coming from FFmpeg? If so, let's just keep the way it is. If it's our new
code, let's be consistent.

[jrummell, 2013/05/03 23:56:21]

Done.

+    uint32_t layer = (buffer[offset + 1] >> 1) & 0x3;
+    uint32_t frequency_index = (buffer[offset + 2] >> 2) & 0xf;
+    uint32_t size = (Read24(buffer + offset + 3) >> 5) & 0x1fff;
+    if (syncword != 0xfff || layer != 0 || frequency_index == 15)
+      return false;
+    offset += size;
+  }
+  return true;

[xhwang, 2013/05/03 19:59:06]

So if buffer_size is <= 5, we return true here. Is this what we wanted?

[jrummell, 2013/05/03 23:56:21]

Done.

+}
+
+// Checks for an AC3 container.
+static bool check_ac3(const uint8_t buffer[], size_t buffer_size) {
+  // AC3 container looks like syncinfo | bsi | audblk * 6 | aux | check.
+  // from spec @ http://www.atsc.org/cms/standards/A52-2012(12-17).pdf
+  size_t offset = 0;
+
+  while (offset + 6 < buffer_size) {
+    // Verify syncinfo (5 bytes)
+    if (Read16(buffer + offset) != 0x0b77)
+      return false;
+    int sample_rate_code = (buffer[offset + 4] >> 6) & 0x03;
+    if (sample_rate_code == 3)  // reserved
+      return false;
+    int frame_size_code = buffer[offset + 4] & 0x3f;
+    if (frame_size_code >= 38)
+      return false;
+
+    // Verify bsi (no fixed alignment)
+    int bit_stream_id = (buffer[offset + 5] >> 3) & 0x1f;
+    if (bit_stream_id >= 10)  // normally 8 or 6
+      return false;
+
+    offset += ac3_frame_size_table[frame_size_code][sample_rate_code];
+  }
+  return true;

[xhwang, 2013/05/03 19:59:06]

ditto

[jrummell, 2013/05/03 23:56:21]

Done.

+}
+
+// Checks for an EAC3 container (very similar to AC3)
+static bool check_eac3(const uint8_t buffer[], size_t buffer_size) {
+  // EAC3 container looks like syncinfo | bsi | audfrm | audblk* | aux | check.
+  // from spec @ http://www.atsc.org/cms/standards/A52-2012(12-17).pdf
+  size_t offset = 0;
+
+  while (offset + 6 < buffer_size) {
+    // Verify syncinfo (5 bytes)
+    if (Read16(buffer + offset) != 0x0b77)
+      return false;
+
+    // Verify bsi (no fixed alignment)
+    int stream_type = (buffer[offset + 2] > 6) & 0x3;
+    if (stream_type == 3)
+      return false;
+    int frame_size = ((Read16(buffer + offset + 2) & 0x7ff) + 1) * 2;
+    if (frame_size < 7)
+      return false;
+    int bit_stream_id = (buffer[offset + 5] >> 3) & 0x1f;
+    if (bit_stream_id != 16)
+      return false;
+
+    offset += frame_size;
+  }
+  return true;

[xhwang, 2013/05/03 19:59:06]

ditto

[jrummell, 2013/05/03 23:56:21]

Done.

+}
+
+// Additional checks for an ACT container.
+static bool check_act(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 512 || Read32(buffer + 16) != 16)
+    return false;
+  // Most of the first 512 bytes should be 0.
+  for (int i = 44; i < 256; ++i)
+    if (buffer[i] != 0)
+      return false;
+  if (buffer[256] != 0x84)
+    return false;
+  for (int i = 264; i < 512; ++i)
+    if (buffer[i] != 0)
+      return false;
+  return true;
+}
+
+// Additional checks for an AEA container.
+static bool check_aea(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 2260)
+    return false;
+  int channels = buffer[264];
+  return ((channels == 1 || channels == 2) &&
+          buffer[2048] == buffer[2259] &&
+          buffer[2049] == buffer[2258]);
+}
+
+// Additional checks for a BINK container.
+static bool check_bink(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 36)
+    return false;
+  uint32_t frames = Read32(buffer + 8);
+  uint32_t width = Read32(buffer + 20);
+  uint32_t height = Read32(buffer + 24);
+  uint32_t fps = Read32(buffer + 28);
+  uint32_t den = Read32(buffer + 32);
+  return (frames > 0 && fps > 0 && den > 0 &&
+          (width > 0 && width <= 7680) &&
+          (height > 0 && height <= 4800));
+}
+
+// Additional checks for a C93 container.
+static bool check_c93(const uint8_t buffer[], size_t buffer_size) {
+  uint16_t index = 1;
+  if (buffer_size < 20)
+    return false;
+  for (int i = 0; i < 16; i += 4) {
+    if (Read16(buffer + i) != index || !buffer[i + 2] || !buffer[i + 3])
+      return false;
+    index += buffer[i + 2];

[xhwang, 2013/05/03 19:59:06]

just double check, so we are not using buffer[i + 3]?

[jrummell, 2013/05/03 23:56:21]

This is what is in ffmpeg
(https://code.google.com/p/chromium/codesearch#chromium/src/third_party/ffmpeg...).

[xhwang, 2013/05/06 23:51:27]

ok, thanks for the link.

[Ilya Sherman, 2013/05/07 00:10:51]

Just double-checking: Is it consistent with ffmpeg's licensing for us to copy
code out of ffmpeg into the Chromium tree?

+    }

[xhwang, 2013/05/03 19:59:06]

indent

[jrummell, 2013/05/03 23:56:21]

Done.

+  return true;
+}
+
+// Additional checks for a CDXL container.
+static bool check_cdxl(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 32)
+    return false;
+  uint8_t type = buffer[0];
+  uint32_t current_size = Read32(buffer + 2);
+  uint32_t width = Read16(buffer + 14);
+  uint32_t height = Read16(buffer + 16);
+  uint8_t plane1 = buffer[18];
+  uint8_t plane2 = buffer[19];
+  uint32_t palette_size = Read16(buffer + 20);
+  uint32_t audio_size = Read16(buffer + 22);
+  uint32_t image_size = width * height * plane2 / 8;
+  return (type == 1 &&
+          palette_size <= 512 &&
+          plane1 != 0 &&
+          plane2 != 0 &&
+          width != 0 &&
+          height != 0 &&
+          current_size >= audio_size + palette_size + image_size + 32 &&
+          Read32(buffer + 24) == 0 &&
+          Read32(buffer + 28) == 0 &&
+          Read16(buffer + 10) == 0);
+}
+
+// Additional checks for a DNXHD container.
+static bool check_dnxhd(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 42)
+    return false;
+  uint32_t height = Read16(buffer + 24);
+  uint32_t width = Read16(buffer + 26);
+  uint32_t compression = Read16(buffer + 40);
+  return (CompareEqual(buffer,
+                       buffer_size,
+                       kDnxhdSignature,
+                       sizeof(kDnxhdSignature) - 1) &&
+          height > 0 && width > 0 && compression >= 1235 &&
+          compression <= 1253);
+}
+
+// Additional checks for a DSICIN container.
+static bool check_dsicin(const uint8_t buffer[], size_t buffer_size) {
+  return (buffer_size > 17 &&
+          Read32(buffer + 12) == 22050 &&
+          buffer[16] == 16 &&
+          buffer[17] == 0);
+}
+
+// Additional checks for an IDCIN container.
+static bool check_idcin(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 20)

[xhwang, 2013/05/03 19:59:06]

s/</<=/ ? It seems we only need 20 bytes.

[jrummell, 2013/05/03 23:56:21]

Correct. If we have 20 bytes we can test. If it's only 19 then we go off the end
of the buffer.

+    return false;
+  uint32_t width = Read32(buffer);
+  uint32_t height = Read32(buffer + 4);
+  uint32_t rate = Read32(buffer + 8);
+  uint32_t bytes = Read32(buffer + 12);
+  uint32_t channels = Read32(buffer + 16);
+  return (width > 0 && width <= 1024 &&
+          height > 0 && height <= 1024 &&
+          rate >= 8000 && rate <= 48000 &&
+          bytes <= 2 &&
+          channels <= 2);
+}
+
+#define HLS1 "#EXT-X-STREAM-INF:"
+#define HLS2 "#EXT-X-TARGETDURATION:"
+#define HLS3 "#EXT-X-MEDIA-SEQUENCE:"

[xhwang, 2013/05/03 19:59:06]

here and 359-362: use const instead of macro?

+
+// Additional checks for a HLS container.
+static bool check_hls(const uint8_t buffer[], size_t buffer_size) {
+  if (CompareEqual(buffer,
+                   buffer_size,
+                   kHlsSignature,
+                   sizeof(kHlsSignature) - 1)) {
+    // Need to find "#EXT-X-STREAM-INF:", "#EXT-X-TARGETDURATION:",
+    // or "#EXT-X-MEDIA-SEQUENCE:" somewhere in the buffer
+    size_t offset = sizeof(kHlsSignature) - 1;
+    while (offset < buffer_size) {
+      if (buffer[offset] == '#') {
+        if (CompareEqual(buffer + offset,
+                         buffer_size - offset,
+                         HLS1,
+                         strlen(HLS1)) ||
+            CompareEqual(buffer + offset,
+                         buffer_size - offset,
+                         HLS2,
+                         strlen(HLS2)) ||
+            CompareEqual(buffer + offset,
+                         buffer_size - offset,
+                         HLS3,
+                         strlen(HLS3)))
+          return true;
+      }
+      ++offset;
+    }
+  }
+  return false;
+}
+
+// Checks for a LOAS container.
+static bool check_loas(const uint8_t buffer[], size_t buffer_size) {
+  // LOAS header is 3 bytes.
+  // (from ISO/IEC 14496-3:2005, page 51)
+  size_t offset = 0;
+  while (offset + 3 < buffer_size) {
+    uint32_t header = Read24(buffer);
+    uint32_t syncword = (header >> 13) & 0x7ff;
+    uint32_t audio_length = (header & 0x1fff);
+    if (syncword != 0x2b7 || audio_length < 4)
+      return false;
+    offset += audio_length + 3 /* header */;
+  }
+  return true;

[xhwang, 2013/05/03 19:59:06]

ditto about buffer_size check

[jrummell, 2013/05/03 23:56:21]

Done.

+}
+
+#define VISUAL_OBJECT_SEQUENCE_START_CODE 0xb0
+#define VISUAL_OBJECT_SEQUENCE_END_CODE 0xb1
+#define VISUAL_OBJECT_START_CODE 0xb5
+#define VOP_START_CODE 0xb6
+
+// Checks for a M4V (raw MPEG4) container.
+static bool check_m4v(const uint8_t buffer[], size_t buffer_size) {
+  // Defined in ISO/IEC 14496-2:2001.
+  // However, no length ... simply scan for start code values
+  // Expect to see SEQ | VO1 | VOL* | VO2 ...
+  size_t offset = 0;
+  int sequence_start_count = 0;
+  int sequence_end_count = 0;
+  int visual_object_count = 0;
+  int vop_count = 0;
+  while (offset + 4 < buffer_size) {
+    uint32_t start_code = Read24(buffer + offset);
+    if (start_code == 1) {
+      // Fail if it is a reserved value.
+      if (buffer[offset] >= 0x30 && buffer[offset] <= 0xaf)
+        return false;
+      if (buffer[offset] >= 0xb7 && buffer[offset] <= 0xb9)
+        return false;
+
+      switch (buffer[offset]) {
+        case VISUAL_OBJECT_SEQUENCE_START_CODE:
+          ++sequence_start_count;
+          break;
+        case VISUAL_OBJECT_SEQUENCE_END_CODE:
+          if (++sequence_end_count > sequence_start_count)
+            return false;
+          break;
+        case VISUAL_OBJECT_START_CODE:
+          ++visual_object_count;
+          break;
+        case VOP_START_CODE:
+          if (++vop_count > visual_object_count)
+            return false;
+          break;
+      }
+      offset += 4;
+    }
+    else {
+      // Start codes can start on any byte boundary
+      ++offset;
+    }
+  }
+  // Not a complete sequence in memory, so return true if we've seen a
+  // visual_object_sequence_start_code and a visual_object_start_code.
+  return (sequence_start_count > 0 && visual_object_count > 0);
+}
+
+// Additional checks for a MM container.
+static bool check_mm(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 16)
+    return false;
+  uint32_t length = Read32(buffer + 2);
+  uint32_t fps = Read16(buffer + 8);
+  uint32_t width = Read16(buffer + 12);
+  uint32_t height = Read16(buffer + 14);
+  uint32_t type = (length + 2 < buffer_size) ? Read16(buffer + length) : 0;

[xhwang, 2013/05/03 19:59:06]

here, length looks like type_offset.. then on line 420, length must be 22 or 24.
so buffer_size should at least be 24?

[jrummell, 2013/05/03 23:56:21]

Done.

+  return ((length == 22 || length == 24) &&
+          fps > 0 && fps <= 60 &&
+          width > 0 && width <= 2048 &&
+          height > 0 && height <= 2048 &&
+          type > 0 && type < 50);
+}
+
+// Additional checks for a MOV container.
+static bool check_mov(const uint8_t buffer[], size_t buffer_size) {

[xhwang, 2013/05/03 19:59:06]

ditto, shall we check buffer_size? 

[jrummell, 2013/05/03 23:56:21]

Done.

+  size_t offset = 0;
+  while (offset + 16 < buffer_size) {
+    uint32_t atomsize = Read32(buffer + offset);
+    uint32_t atomtype = Read32(buffer + offset + 4);
+    // Valid atoms from http://www.mp4ra.org/atoms.html
+    switch (atomtype) {
+      case TAG('a','i','n','f'):
+      case TAG('a','v','c','n'):
+      case TAG('b','l','o','c'):
+      case TAG('b','p','c','c'):
+      case TAG('b','u','f','f'):
+      case TAG('b','x','m','l'):
+      case TAG('c','c','i','d'):
+      case TAG('c','d','e','f'):
+      case TAG('c','m','a','p'):
+      case TAG('c','o','6','4'):
+      case TAG('c','o','l','r'):
+      case TAG('c','r','h','d'):
+      case TAG('c','s','l','g'):
+      case TAG('c','t','t','s'):
+      case TAG('c','v','r','u'):
+      case TAG('d','i','n','f'):
+      case TAG('d','r','e','f'):
+      case TAG('d','s','g','d'):
+      case TAG('d','s','t','g'):
+      case TAG('e','d','t','s'):
+      case TAG('e','l','s','t'):
+      case TAG('f','e','c','i'):
+      case TAG('f','e','c','r'):
+      case TAG('f','i','i','n'):
+      case TAG('f','i','r','e'):
+      case TAG('f','p','a','r'):
+      case TAG('f','r','e','e'):
+      case TAG('f','r','m','a'):
+      case TAG('f','t','y','p'):
+      case TAG('g','i','t','n'):
+      case TAG('g','r','p','i'):
+      case TAG('h','d','l','r'):
+      case TAG('h','m','h','d'):
+      case TAG('h','p','i','x'):
+      case TAG('i','c','n','u'):
+      case TAG('I','D','3','2'):
+      case TAG('i','d','a','t'):
+      case TAG('i','h','d','r'):
+      case TAG('i','i','n','f'):
+      case TAG('i','l','o','c'):
+      case TAG('i','m','i','f'):
+      case TAG('i','n','f','u'):
+      case TAG('i','o','d','s'):
+      case TAG('i','p','h','d'):
+      case TAG('i','p','m','c'):
+      case TAG('i','p','r','o'):
+      case TAG('i','r','e','f'):
+      case TAG('j','P',' ',' '):
+      case TAG('j','p','2','c'):
+      case TAG('j','p','2','h'):
+      case TAG('j','p','2','i'):
+      case TAG('l','r','c','u'):
+      case TAG('m','7','h','d'):
+      case TAG('m','d','a','t'):
+      case TAG('m','d','h','d'):
+      case TAG('m','d','i','a'):
+      case TAG('m','d','r','i'):
+      case TAG('m','e','c','o'):
+      case TAG('m','e','h','d'):
+      case TAG('m','e','r','e'):
+      case TAG('m','e','t','a'):
+      case TAG('m','f','h','d'):
+      case TAG('m','f','r','a'):
+      case TAG('m','f','r','o'):
+      case TAG('m','i','n','f'):
+      case TAG('m','j','h','d'):
+      case TAG('m','o','o','f'):
+      case TAG('m','o','o','v'):
+      case TAG('m','v','c','g'):
+      case TAG('m','v','c','i'):
+      case TAG('m','v','e','x'):
+      case TAG('m','v','h','d'):
+      case TAG('m','v','r','a'):
+      case TAG('n','m','h','d'):
+      case TAG('o','c','h','d'):
+      case TAG('o','d','a','f'):
+      case TAG('o','d','d','a'):
+      case TAG('o','d','h','d'):
+      case TAG('o','d','h','e'):
+      case TAG('o','d','r','b'):
+      case TAG('o','d','r','m'):
+      case TAG('o','d','t','t'):
+      case TAG('o','h','d','r'):
+      case TAG('p','a','d','b'):
+      case TAG('p','a','e','n'):
+      case TAG('p','c','l','r'):
+      case TAG('p','d','i','n'):
+      case TAG('p','i','t','m'):
+      case TAG('r','e','s',' '):
+      case TAG('r','e','s','c'):
+      case TAG('r','e','s','d'):
+      case TAG('s','b','g','p'):
+      case TAG('s','c','h','i'):
+      case TAG('s','c','h','m'):
+      case TAG('s','d','e','p'):
+      case TAG('s','d','h','d'):
+      case TAG('s','d','t','p'):
+      case TAG('s','d','v','p'):
+      case TAG('s','e','g','r'):
+      case TAG('s','e','n','c'):
+      case TAG('s','g','p','d'):
+      case TAG('s','i','d','x'):
+      case TAG('s','i','n','f'):
+      case TAG('s','k','i','p'):
+      case TAG('s','m','h','d'):
+      case TAG('s','r','m','b'):
+      case TAG('s','r','m','c'):
+      case TAG('s','r','p','p'):
+      case TAG('s','t','b','l'):
+      case TAG('s','t','c','o'):
+      case TAG('s','t','d','p'):
+      case TAG('s','t','h','d'):
+      case TAG('s','t','s','c'):
+      case TAG('s','t','s','d'):
+      case TAG('s','t','s','h'):
+      case TAG('s','t','s','s'):
+      case TAG('s','t','s','z'):
+      case TAG('s','t','t','s'):
+      case TAG('s','t','y','p'):
+      case TAG('s','t','z','2'):
+      case TAG('s','u','b','s'):
+      case TAG('s','w','t','c'):
+      case TAG('t','f','a','d'):
+      case TAG('t','f','h','d'):
+      case TAG('t','f','m','a'):
+      case TAG('t','f','r','a'):
+      case TAG('t','i','b','r'):
+      case TAG('t','i','r','i'):
+      case TAG('t','k','h','d'):
+      case TAG('t','r','a','f'):
+      case TAG('t','r','a','k'):
+      case TAG('t','r','e','f'):
+      case TAG('t','r','e','x'):
+      case TAG('t','r','g','r'):
+      case TAG('t','r','i','k'):
+      case TAG('t','r','u','n'):
+      case TAG('u','d','t','a'):
+      case TAG('u','i','n','f'):
+      case TAG('U','I','T','S'):
+      case TAG('u','l','s','t'):
+      case TAG('u','r','l',' '):
+      case TAG('u','u','i','d'):
+      case TAG('v','m','h','d'):
+      case TAG('v','w','d','i'):
+      case TAG('x','m','l',' '):
+      case TAG('C','o','d','e'):
+      case TAG('a','l','b','m'):
+      case TAG('a','n','g','l'):
+      case TAG('a','u','t','h'):
+      case TAG('c','l','f','n'):
+      case TAG('c','l','i','d'):
+      case TAG('c','l','s','f'):
+      case TAG('c','m','i','d'):
+      case TAG('c','m','n','m'):
+      case TAG('c','o','l','l'):
+      case TAG('c','p','r','t'):
+      case TAG('d','a','t','e'):
+      case TAG('d','s','c','p'):
+      case TAG('g','n','r','e'):
+      case TAG('h','n','t','i'):
+      case TAG('k','y','w','d'):
+      case TAG('l','o','c','i'):
+      case TAG('m','a','n','u'):
+      case TAG('m','o','d','l'):
+      case TAG('p','e','r','f'):
+      case TAG('r','e','e','l'):
+      case TAG('r','t','n','g'):
+      case TAG('s','c','e','n'):
+      case TAG('s','h','o','t'):
+      case TAG('s','l','n','o'):
+      case TAG('s','t','r','k'):
+      case TAG('t','h','m','b'):
+      case TAG('t','s','e','l'):
+      case TAG('t','i','t','l'):
+      case TAG('u','r','a','t'):
+      case TAG('y','r','r','c'):
+      case TAG('c','l','i','p'):
+      case TAG('c','r','g','n'):
+      case TAG('c','t','a','b'):
+      case TAG('d','c','f','D'):
+      case TAG('e','l','n','g'):
+      case TAG('i','m','a','p'):
+      case TAG('k','m','a','t'):
+      case TAG('l','o','a','d'):
+      case TAG('m','a','t','t'):
+      case TAG('p','n','o','t'):
+      case TAG('w','i','d','e'):
+        break;
+      default:
+        return false;
+    }
+    if (atomsize == 0)
+      break;  // indicates the last atom
+    if (atomsize == 1) {
+      // Indicates that the length is the next 64bits.
+      if (Read32(buffer + offset + 8) != 0)
+        break;  // offset is way past buffer size
+      atomsize = Read32(buffer + offset + 12);
+    }
+    offset += atomsize;
+  }
+  return true;
+}
+
+enum MPEGVersion {
+  Version25 = 0,
+  v_reserved,
+  Version2,
+  Version1
+};
+enum MPEGlayer {
+  l_reserved = 0,
+  Layer3,
+  Layer2,
+  Layer1
+};
+
+static int Sample_Rate_Table[4][4] = {
+  { 11025, 12000, 8000, 0 },  // v2.5
+  { 0, 0, 0, 0 },             // not used
+  { 22050, 24000, 16000, 0 }, // v2
+  { 44100, 48000, 32000, 0 }  // v1
+};
+
+static int Bit_Rate_Table_v1_l1[16] =
+  { 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0 };

[xhwang, 2013/05/03 19:59:06]

here and below, 4 space indentation.

[jrummell, 2013/05/03 23:56:21]

Reformatted to what clang-format does.

+static int Bit_Rate_Table_v1_l2[16] =
+  { 0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 0 };
+static int Bit_Rate_Table_v1_l3[16] =
+  { 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0 };
+static int Bit_Rate_Table_v2_l1[16] =
+  { 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0 };
+static int Bit_Rate_Table_v2_l23[16] =
+  { 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 };
+
+static bool valid_mpeg_audio_frame_header(uint32_t header, size_t* framesize) {
+  *framesize = 0;
+  // first 11 bits must be all set
+  if ((header & 0xffe00000) != 0xffe00000)
+    return false;
+  // version (bits 20-19) can not be 01
+  int version = (header >> 19) & 0x3;
+  if (version == 1)
+    return false;
+  // layer (bits 18-17) can not be 00
+  int layer = (header >> 17) & 0x3;
+  if (layer == 0)
+    return false;
+  // bitrate (bits 15-12) can not be 1111
+  int bitrate_index = (header >> 12) & 0xf;
+  if (bitrate_index == 0xf)
+    return false;
+  // sampling (bits 11-10) can not be 11
+  int sampling_index = (header >> 10) & 0x3;
+  if (sampling_index == 3)
+    return false;
+
+  // Frame size:
+  // For Layer I files = (12 * BitRate / SampleRate + Padding) * 4
+  // For others = 144 * BitRate / SampleRate + Padding
+  // Unfortunately, BitRate and SampleRate are coded
+  int padding = (header >> 9) & 0x1;
+  int sampling_rate = Sample_Rate_Table[version][sampling_index];
+  int bitrate;
+  if (version == Version1) {
+    if (layer == Layer1)
+      bitrate = Bit_Rate_Table_v1_l1[bitrate_index];
+    else if (layer == Layer2)
+      bitrate = Bit_Rate_Table_v1_l2[bitrate_index];
+    else
+      bitrate = Bit_Rate_Table_v1_l3[bitrate_index];
+  }
+  else {
+    if (layer == Layer1)
+      bitrate = Bit_Rate_Table_v2_l1[bitrate_index];
+    else
+      bitrate = Bit_Rate_Table_v2_l23[bitrate_index];
+  }
+  if (layer == Layer1)
+    *framesize = ((12000 * bitrate) / sampling_rate + padding) * 4;
+  else
+    *framesize = (144000 * bitrate) / sampling_rate + padding;
+  return (bitrate > 0 && sampling_rate > 0);
+}
+
+// Extract a size encoded the MP3 way
+static uint32_t get_mp3_header_size(const uint8_t buffer[]) {
+  uint32_t size = ((buffer[6] & 0x7f) << 21) +
+                  ((buffer[7] & 0x7f) << 14) +
+                  ((buffer[8] & 0x7f) << 7) +
+                   (buffer[9] & 0x7f) +

[xhwang, 2013/05/03 19:59:06]

indent

[jrummell, 2013/05/03 23:56:21]

Done.

+                    10;
+  if (buffer[5] & 0x10)  // footer added?
+    size += 10;
+  return size;
+}
+
+// Additional checks for a MP3 container.
+static bool check_mp3(const uint8_t buffer[],
+                      size_t buffer_size,
+                      bool seenHeader) {

[xhwang, 2013/05/03 19:59:06]

ditto, check buffer_size?

[jrummell, 2013/05/03 23:56:21]

Not sure why? We only return true if we see at least 10 headers, so if it's too
small it won't match.

+  size_t framesize;
+  size_t numSeen = 0;
+  size_t offset = 0;
+  if (seenHeader)
+    offset = get_mp3_header_size(buffer);
+  while (offset + 3 <= buffer_size &&
+         valid_mpeg_audio_frame_header(Read32(buffer + offset), &framesize)) {
+    ++numSeen;
+    offset += framesize;
+  }
+  return (numSeen > 10 || offset >= buffer_size);
+}
+
+// Extract an encoded MPC size, returning the value and
+// the number of characters used by the size.
+static int64_t get_mpc8_header_size(const uint8_t* b, size_t* count) {

[xhwang, 2013/05/03 19:59:06]

s/b/buffer and s/count/buffer_size to be consistent?

[jrummell, 2013/05/03 23:56:21]

Done s/b/buffer. However, the second is the number processed, not the buffer
size.

+  int64_t size = 0;
+  uint8_t c;
+  *count = 0;
+  do {
+    c = *b++;
+    if (++(*count) > 10)
+      return -1;
+    size = (size << 7) | (c & 0x7f);
+  } while (c & 0x80);
+  return size;
+}
+
+// Additional checks for a MPC8 container.
+static bool check_mpc8(const uint8_t buffer[], size_t buffer_size) {
+  size_t offset = 4;
+  while (offset < buffer_size - 14) {

[xhwang, 2013/05/03 19:59:06]

size_t -14 is dangerous.

[jrummell, 2013/05/03 23:56:21]

Done.

+    if (!isupper(buffer[offset]) || !isupper(buffer[offset + 1]))

[xhwang, 2013/05/03 19:59:06]

include what you use, add #include <cctype> ?

[jrummell, 2013/05/03 23:56:21]

Done.

+      return false;
+
+    size_t size_characters;
+    int64_t size = get_mpc8_header_size(buffer + offset, &size_characters);
+    if (size < 2)
+      return false;
+    if (buffer[offset] == 'S' && buffer[offset + 1] == 'H') {
+      return (size >= 11 && size <= 28 &&
+              Read32(buffer + offset + size_characters + 2) != 0);
+    }
+    offset = offset + size + size_characters;
+  }
+  return false;
+}
+
+// Additional checks for a MSNWCTCP container.
+static bool check_msnwctcp(const uint8_t buffer[], size_t buffer_size) {
+  // The FFmpeg probe scans through the complete buffer looking for
+  // a matching header. This code only looks for it at the beginning
+  // of the buffer.
+  uint32_t width = Read16(buffer + 2);

[xhwang, 2013/05/03 19:59:06]

check buffer_size before starting to read?

[jrummell, 2013/05/03 23:56:21]

All the checks tagged with "Additional" are only called from
LookupContainerByFirst4, so we know the size is at least 12 bytes. But it
doesn't hurt to make it explicit.

+  uint32_t height = Read16(buffer + 4);
+  if (!(width == 320 && height == 240) && !(width == 160 && height == 120))
+    return false;
+  return (buffer_size > 16 && Read32(buffer + 12) != TAG('M','L','2','0'));
+}
+
+// Additional checks for a MTV container.
+static bool check_mtv(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 58)
+    return false;
+  uint32_t bpp = Read16(buffer + 50);
+  if (bpp != 16)
+    return false;
+  uint32_t width = Read16(buffer + 52);
+  uint32_t height = Read16(buffer + 54);
+  uint32_t segment_size = Read16(buffer + 56);
+  return ((width != 0 && height != 0) || (segment_size != 0));
+}
+
+// Additional checks for a NC container.
+static bool check_nc(const uint8_t buffer[], size_t buffer_size) {
+  uint32_t size = Read16(buffer + 5);

[xhwang, 2013/05/03 19:59:06]

check buffer_size before reading?

[jrummell, 2013/05/03 23:56:21]

Done.

+  return (size + 20 < buffer_size && Read32(buffer + size + 16) == 0x1a5);
+}
+
+// Additional checks for a NSV container, only if the header isn't
+// at the start of the file.
+static bool check_nsv(const uint8_t buffer[], size_t buffer_size) {
+  // Get the chunk size and check if at the end we are getting 0xBEEF
+  if (buffer_size < 24)
+    return false;
+  size_t vsize = Read24(buffer + 19) >> 4;
+  size_t asize = Read16(buffer + 22);
+  size_t offset = 24 + asize + vsize;
+  return (offset + 2 <= buffer_size && Read16(buffer + offset) == 0xbeef);
+}
+
+// Additional checks for an OMA container.
+static bool check_oma(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer[4] != 0)

[xhwang, 2013/05/03 19:59:06]

check buffer_size before read?

[jrummell, 2013/05/03 23:56:21]

Done.

+    return false;
+  uint32_t tag_len = get_mp3_header_size(buffer);
+  if (tag_len > buffer_size - 6)
+    return false;
+  return (Read24(buffer + tag_len) == TAG(0,'E','A','3') &&
+          buffer[tag_len + 4] == 0 && buffer[tag_len + 5] == 96);
+}
+
+// Additional checks for a PJS container.
+static bool check_pjs(const uint8_t buffer[], size_t buffer_size) {
+  size_t offset = 0;
+  while (buffer[offset] != '"' && offset < buffer_size - 2)
+    ++offset;
+  ++offset;
+  while (buffer[offset] != '"' && offset < buffer_size) {
+    if (buffer[offset] == '\n' || buffer[offset] == '\r')
+      return false;
+    ++offset;
+  }
+  return true;
+}
+
+// Additional checks for a PVA container.
+static bool check_pva(const uint8_t buffer[], size_t buffer_size) {
+  uint32_t length = Read16(buffer + 6);
+  if (buffer[4] != 0x55 || (buffer[5] & 0xe0) != 0 || length > 6136)
+    return false;
+  if (buffer_size < length + 8)
+    return false;
+  return (buffer[length] == 'A' &&
+          buffer[length + 1] == 'V' &&
+          (buffer[length + 2] == 1 || buffer[length + 2] == 2) &&
+          buffer[length + 4] == 0x55 &&
+          (buffer[5] & 0xe0) == 0 &&
+          Read16(buffer + length + 6) <= 6136);
+}
+
+// Additional checks for a TIERTEXSEQ container.
+static bool check_tiertexseq(const uint8_t buffer[], size_t buffer_size) {
+  // No real header, but first 256 bytes are always 0
+  if (buffer_size < 257)
+    return false;
+  for (int i = 0; i < 256; ++i)
+    if (buffer[i] != 0)
+      return false;
+  return (buffer[256] != 0 && buffer[257] != 0);
+}
+
+// Additional checks for a TMV container.
+static bool check_tmv(const uint8_t buffer[], size_t buffer_size) {
+  return (Read16(buffer + 4) >= 5000 &&   // sample rate
+          Read16(buffer + 6) >= 41 &&     // audio size
+          buffer[8] == 0 &&               // compression method
+          buffer[9] != 0 &&               // width
+          buffer[10] != 0);               // height
+}
+
+// Additional checks for a VIVO container.
+static bool check_vivo(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer[0] != 0)
+    return false;
+  uint32_t length = buffer[1] & 0x7f;
+  size_t offset = 2;
+  if ((buffer[1] & 0x80) != 0) {
+    if (buffer[2] & 0x80)
+      return false;
+    length = (length << 7) + (buffer[2] & 0x7f);
+    offset = 3;
+  }
+  if (length < 21 || length > 1024 || offset + 16 > buffer_size)
+    return false;
+  return (CompareEqual(buffer + offset,
+                       buffer_size - offset,
+                       kVivoSignature,
+                       sizeof(kVivoSignature) - 1) &&
+          buffer[offset + 16] >= '0' && buffer[offset + 16] <= '2');
+}
+
+// Additional checks for a VMD container.
+static bool check_vmd(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 16)
+    return false;
+  uint32_t width = Read16(buffer + 12);
+  uint32_t height = Read16(buffer + 14);
+  return (width > 0 && width <= 2048 && height > 0 && height <= 2048);
+}
+
+// Additional checks for a VQF container.
+static bool check_vqf(const uint8_t buffer[], size_t buffer_size) {
+  return (CompareEqual(buffer + 4, buffer_size - 4, "97012000", 8) ||
+          CompareEqual(buffer + 4, buffer_size - 4, "00052200", 8));
+}
+
+// Read a Matroska TAG, updating offset to point past it.
+static int get_vtag(const uint8_t buffer[], size_t* offset) {
+  // Size of the tag is determined the same way as VINT,
+  // but the bit is not removed. Maximum of 4 bytes.
+  int result = buffer[*offset];
+  if ((result & 0x80) != 0) {
+    // It is a one byte tag
+    ++*offset;
+  }
+  else if ((result & 0x40) != 0) {
+    // It is a 2 byte tag
+    result = Read16(buffer + *offset);
+    *offset += 2;
+  }
+  else if ((result & 0x20) != 0) {
+    // It is a 3 byte tag
+    result = Read24(buffer + *offset);
+    *offset += 3;
+  }
+  else {
+    // It is a 4 byte tag
+    result = Read32(buffer + *offset);
+    *offset += 4;
+  }
+  return result;
+}
+
+// Read a Matroska VINT, updating offset to point past it.
+static int get_vint(const uint8_t buffer[], size_t* offset) {
+  // Length = 1 + [number_of_leading_zero_bits].
+  int size = 1;
+  int mask = 0x80;
+  uint8_t b = buffer[*offset];
+  while (mask > 0 && (b & mask) == 0) {
+    ++size;
+    mask = mask >> 1;
+  }
+
+  // Now that we know the size, use the remaining bits plus
+  // following bytes to get the value.
+  int result = buffer[(*offset)++] & (mask - 1);
+  while (--size > 0)
+    result = (result << 8) | buffer[(*offset)++];
+  return result;
+}
+
+// Additional checks for a WEBM container.
+static bool check_webm(const uint8_t buffer[], size_t buffer_size) {
+  size_t offset = 4;
+  int header_size = get_vint(buffer, &offset);
+  size_t lastoffset = offset + header_size;
+  if (lastoffset > buffer_size)
+    return false;
+  while (offset < lastoffset) {
+    int tag = get_vtag(buffer, &offset);
+    int tagsize = get_vint(buffer, &offset);
+    switch (tag) {
+      case 0x4286:  // EBMLVersion
+      case 0x42f7:  // EBMLReadVersion
+      case 0x42f2:  // EBMLMaxIdLength
+      case 0x42f3:  // EBMLMaxSizeLength
+      case 0x4287:  // DocTypeVersion
+      case 0x4285:  // DocTypeReadVersion
+      case 0xec:    // void
+      case 0xbf:    // CRC32
+        offset += tagsize;
+        break;
+      case 0x4282:  // EBMLDocType
+        return (
+            (tagsize >= 4 &&
+             CompareEqual(buffer + offset, buffer_size - offset, "webm", 4)) ||
+            (tagsize >= 8 &&
+             CompareEqual(
+                 buffer + offset, buffer_size - offset, "matroska", 8)));
+      default:
+        // Unrecognized tag
+        return false;
+    }
+  }
+  return false;
+}
+
+// Additional checks for a WSAUD container.
+static bool check_wsaud(const uint8_t buffer[], size_t buffer_size) {
+  uint32_t sample_rate = Read16(buffer);
+  if (sample_rate < 8000 || sample_rate > 48000)
+    return false;
+  if ((buffer[10] & 0xfc) != 0 || (buffer[11] != 1 && buffer[11] != 99))
+    return false;
+  return (buffer_size > 20 && Read32(buffer + 16) == 0x0000deaf);
+}
+
+// Additional checks for a XA container.
+static bool check_xa(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 14)
+    return false;
+  uint32_t channels = Read16(buffer + 10);
+  if (channels < 1 || channels > 8)
+    return false;
+  uint32_t srate = Read16(buffer + 12);
+  if (srate < 1 || srate > 192000)
+    return false;
+  uint32_t bits_per_sample = Read16(buffer + 10);
+  return (bits_per_sample >= 4 || bits_per_sample <= 32);
+}
+
+// Additional checks for a XBIN container.
+static bool check_xbin(const uint8_t buffer[], size_t buffer_size) {
+  uint32_t x = Read16(buffer + 5);
+  return (buffer[4] == 0x1a &&
+          x > 0 && x <= 160 &&
+          buffer[9] > 0 && buffer[9] <= 32);
+}
+
+// Additional checks for a XMV container.
+static bool check_xmv(const uint8_t buffer[], size_t buffer_size) {
+  if (buffer_size < 18)
+    return false;
+  uint32_t version = Read16(buffer + 16);
+  return (Read32(buffer + 12) == TAG('x','o','b','X') &&
+          version > 0 && version <= 4);
+}
+
+// Additional checks for a YOP container.
+static bool check_yop(const uint8_t buffer[], size_t buffer_size) {
+  return (buffer_size > 20 &&
+          buffer[2] < 10 &&
+          buffer[3] < 10 &&
+          buffer[6] != 0 &&
+          buffer[7] != 0 &&
+          (buffer[8] & 1) == 0 &&
+          (buffer[10] & 1) == 0 &&
+          Read16(buffer + 18) >= 920 &&
+          Read16(buffer + 18) <
+              static_cast<uint32_t>(buffer[12] * 3 + 4 + buffer[7] * 2048));
+}
+
+// Attempt to determine the container type from the buffer provided. This is
+// a simple pass, that uses the first 4 bytes of the buffer as an index to get
+// a rough idea of the container format. It covers the following containers
+// (those with * are not fully covered):
+//   4xm, act, aea, aiff, amr, anm, apc, ape, aqtitle, asf, ass, ast, au, avi,
+//   avr, avs, bethsoftvid, bfi, bink, bit, brstm, c93, caff, cdxl, concat,
+//   dfa, dnxhd, dsicin, dtshd, dxa, ea, epaf, ffm, ffmetadata, file_cpk, flac,
+//   flic, flv, frm, gif, gxf, hls, ico, idf, iff, ilbc, ircam, iss, iv8, ivf,
+//   jv, libnut, lmlm4, lvf, lxf, mgsts, mm, mmf, mov, mp3*, mpc, mpc8,
+//   msnwctcp*, mtv, mv, nc, nistsphere, nsv*, nut, nuv, ogg, oma, paf, pmp,
+//   pva, pvf, qcp, r3d, realtext, rl2, rm, roq, rpl, sami, siff, smjpeg, smk,
+//   smush, sol, sox, swf, tak, thp, tiertexseq, tmv, tta, txd, vc1test, vivo,
+//   vmd, vobsub, voc, vqf, w64, wav, wc3movie, webm, webvtt, wsaud, wsvqa,
+//   wtv, wv, xa, xbin, xmv, xwma, yop, yuv4mpegpipe
+static FFmpegContainerName LookupContainerByFirst4(const uint8 buffer[],
+                                                   size_t buffer_size) {
+  // Minimum size that the code expects to exist without checking size.
+  if (buffer_size < 12)
+    return CONTAINER_UNKNOWN;
+
+  uint32_t first4 = Read32(buffer);
+  uint32_t second4 = Read32(buffer + 4);
+  uint32_t third4 = Read32(buffer + 8);
+  uint32_t next;
+
+  switch (first4) {
+    case 0:
+      if (buffer_size > 16 &&
+          Read16(buffer + 4) == 0x1bc &&
+          Read32(buffer + 10) == 0 &&
+          Read16(buffer + 14) == 0xe1e2)
+        return CONTAINER_GXF;
+      if (check_mm(buffer, buffer_size))
+        return CONTAINER_MM;
+      if (second4 > 0 && second4 <= 1024 * 1024 && Read24(buffer + 8) == 1)
+        return CONTAINER_LMLM4;
+      if (check_tiertexseq(buffer, buffer_size))
+        return CONTAINER_TIERTEXSEQ;
+      break;
+    case 1:
+      if (second4 > 0 && second4 <= 1024 * 1024 && Read24(buffer + 8) == 1)
+        return CONTAINER_LMLM4;
+      if (Read16(buffer + 4) != 0)
+        return CONTAINER_ICO;
+      break;
+    case 2:
+      if (second4 > 0 && second4 <= 1024 * 1024 && Read24(buffer + 8) == 1)
+        return CONTAINER_LMLM4;
+      break;
+    case 4:
+      if (second4 > 0 && second4 <= 1024 * 1024 &&
+          (Read16(buffer + 8) & 0xfffe) == 0xfffc)
+        return CONTAINER_LMLM4;
+      break;
+    case 0xe:
+      if (buffer_size > 16 && second4 == 0x50 && Read32(buffer + 12) == 0x34)
+        return CONTAINER_MGSTS;
+      break;
+    case 0x16:
+      if (third4 == 0x1803ffff || third4 == 0x1003ffff)
+        return CONTAINER_TXD;
+      break;
+    case 0x1a5:
+      if (check_nc(buffer, buffer_size))
+        return CONTAINER_NC;
+      break;
+    case TAG('\x00','\x00','\x02','\x80'):
+      if (check_dnxhd(buffer, buffer_size))
+        return CONTAINER_DNXHD;
+      break;
+    case 0x800:
+      if (check_aea(buffer, buffer_size))
+        return CONTAINER_AEA;
+      break;
+    case 0x001800a0:
+    case 0x00180140:
+      if (check_msnwctcp(buffer, buffer_size))
+        return CONTAINER_MSNWCTCP;
+      break;
+    case TAG('\x00','\x0a','S','M'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kSmjpegSignature,
+                       sizeof(kSmjpegSignature) - 1))
+        return CONTAINER_SMJPEG;
+    break;
+    case 0x1084ffff:
+      if (Read16(buffer + 4) == 0xffff)
+        return CONTAINER_ROQ;
+      break;
+    case TAG('\x01','\x01','\x03','\xb8'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kIv8Signature,
+                       sizeof(kIv8Signature) - 1))
+        return CONTAINER_IV8;
+      break;
+    case TAG('\x04','\x31','\x2e','\x34'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kIdfSignature,
+                       sizeof(kIdfSignature) - 1))
+        return CONTAINER_IDF;
+      break;
+    case TAG('\x0b','\x8d','S','O'):
+    case TAG('\x0c','\x0d','S','O'):
+    case TAG('\x0c','\x8d','S','O'):
+      if (buffer[4] == 'L' && buffer[5] == 0)
+        return CONTAINER_SOL;
+      break;
+    case 0x1a45dfa3:
+      if (check_webm(buffer, buffer_size))
+        return CONTAINER_WEBM;
+      break;
+    case TAG('.','s','n','d'):
+      return CONTAINER_AU;
+    case TAG('\x30','\x26','\xB2','\x75'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kAsfSignature,
+                       sizeof(kAsfSignature) - 1))
+        return CONTAINER_ASF;
+      break;
+    case TAG(' ','p','a','f'):
+      if (buffer_size > 24 &&
+          second4 == 0 && third4 == 0 &&
+          Read32(buffer + 12) != 0 &&
+          Read32(buffer + 20) != 0)
+        return CONTAINER_EPAF;
+      break;
+    case TAG('#','!','A','M'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kAmrSignature,
+                       sizeof(kAmrSignature) - 1))
+        return CONTAINER_AMR;
+      break;
+    case TAG('#','!','i','L'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kIlbcSignature,
+                       sizeof(kIlbcSignature) - 1))
+        return CONTAINER_ILBC;
+      break;
+    case TAG('#','E','X','T'):
+      if (check_hls(buffer, buffer_size))
+        return CONTAINER_HLS;
+      break;
+    case TAG('#',' ','V','o'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kVobsubSignature,
+                       sizeof(kVobsubSignature) - 1))
+        return CONTAINER_VOBSUB;
+      break;
+    case TAG('.','R','M','F'):
+      if (buffer[4] == 0 && buffer[5] == 0)
+        return CONTAINER_RM;
+      break;
+    case TAG('.','r','a','\xfd'):
+      return CONTAINER_RM;
+    case TAG('.','S','o','X'):
+    case TAG('X','o','S','.'):
+      return CONTAINER_SOX;
+    case TAG('1','S','N','h'):
+    case TAG('S','C','H','l'):
+    case TAG('S','E','A','D'):
+    case TAG('S','H','E','N'):
+    case TAG('k','V','G','T'):
+    case TAG('M','A','D','k'):
+    case TAG('M','P','C','h'):
+    case TAG('M','V','h','d'):
+      if ((second4 > 0x0fffff) && ((second4 & 0x0f0ff) != 0))
+        return CONTAINER_EA;
+      break;
+    case TAG('2','B','I','T'):
+      return CONTAINER_AVR;
+    case TAG('A','N','I','M'):
+      if (third4 == TAG('A','H','D','R'))
+        return CONTAINER_SMUSH;
+      break;
+    case TAG('A','R','M','o'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kRplSignature,
+                       sizeof(kRplSignature) - 1))
+        return CONTAINER_RPL;
+      break;
+    case TAG('B','B','C','D'):
+      return CONTAINER_DIRAC;
+    case TAG('B','F','&','I'):
+      return CONTAINER_BFI;
+    case TAG(';','F','F','M'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kFfSignature,
+                       sizeof(kFfSignature) - 1))
+        return CONTAINER_FFMETADATA;
+      break;
+    case TAG('B','I','K','b'):
+    case TAG('B','I','K','f'):
+    case TAG('B','I','K','g'):
+    case TAG('B','I','K','h'):
+    case TAG('B','I','K','i'):
+      if (check_bink(buffer, buffer_size))
+        return CONTAINER_BINK;
+      break;
+    case TAG('c','a','f','f'):
+      if (Read16(buffer + 4) == 1)
+        return CONTAINER_CAF;
+      break;
+    case TAG('C','r','e','a'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kVocSignature,
+                       sizeof(kVocSignature) - 1))
+        return CONTAINER_VOC;
+      break;
+    case TAG('C','R','Y','O'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kApcSignature,
+                       sizeof(kApcSignature) - 1))
+        return CONTAINER_APC;
+      break;
+    case TAG('D','E','X','A'):
+      if (buffer_size > 15 &&
+          Read16(buffer + 11) <= 2048 &&
+          Read16(buffer + 13) <= 2048)
+        return CONTAINER_DXA;
+      break;
+    case TAG('D','K','I','F'):
+      if (second4 == 32)
+        return CONTAINER_IVF;
+      break;
+    case TAG('D','T','S','H'):
+      if (second4 == TAG('D','H','D','R'))
+        return CONTAINER_DTSHD;
+      break;
+    case TAG('D','F','I','A'):
+      return CONTAINER_DFA;
+    case TAG('\x64','\xa3','\x01','\x00'):
+    case TAG('\x64','\xa3','\x02','\x00'):
+    case TAG('\x64','\xa3','\x03','\x00'):
+    case TAG('\x64','\xa3','\x04','\x00'):
+    case TAG('\x00','\x01','\xa3','\x64'):
+    case TAG('\x00','\x02','\xa3','\x64'):
+    case TAG('\x00','\x03','\xa3','\x64'):
+      if (second4 != 0 && third4 != 0)
+        return CONTAINER_IRCAM;
+      break;
+    case TAG('e','a','3','\x03'):
+      if (check_oma(buffer, buffer_size))
+        return CONTAINER_OMA;
+      break;
+    case TAG('f','a','p',' '):
+      if (buffer_size > 24 &&
+          second4 == 0 && third4 == 1 &&
+          Read32(buffer + 12) != 0 &&
+          Read32(buffer + 20) != 0)
+        return CONTAINER_EPAF;
+      break;
+    case TAG('f','f','c','o'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kConcatSignature,
+                       sizeof(kConcatSignature) - 1))
+        return CONTAINER_CONCAT;
+      break;
+    case TAG('F','F','M','1'):
+    case TAG('F','F','M','2'):
+      return CONTAINER_FFM;
+    case TAG('F','I','L','M'):
+      return CONTAINER_FILM_CPK;
+    case TAG('f','L','a','C'):
+      return CONTAINER_FLAC;
+    case TAG('F','L','V','\x00'):
+    case TAG('F','L','V','\x01'):
+    case TAG('F','L','V','\x02'):
+    case TAG('F','L','V','\x03'):
+    case TAG('F','L','V','\x04'):
+      if (buffer[5] == 0 && Read32(buffer + 5) > 8)
+        return CONTAINER_FLV;
+      break;
+    case TAG('F','O','R','M'):
+      switch (third4) {
+        case TAG('A','I','F','F'):
+        case TAG('A','I','F','C'):
+          return CONTAINER_AIFF;
+        case TAG('8','S','V','X'):
+        case TAG('1','6','S','V'):
+        case TAG('M','A','U','D'):
+        case TAG('P','B','M',' '):
+        case TAG('A','C','B','M'):
+        case TAG('D','E','E','P'):
+        case TAG('I','L','B','M'):
+        case TAG('R','G','B','8'):
+        case TAG('R','G','B','N'):
+          return CONTAINER_IFF;
+        case TAG('M','O','V','E'):
+          return CONTAINER_WC3MOVIE;
+        case TAG('R','L','V','2'):
+        case TAG('R','L','V','3'):
+          return CONTAINER_RL2;
+        case TAG('W','V','Q','A'):
+          return CONTAINER_WSVQA;
+      }
+      break;
+    case TAG('G','I','F','8'):
+      if ((buffer[4] == '7' || buffer[4] == '9') &&
+          buffer[5] == 'a' &&
+          Read16(buffer + 6) != 0 &&
+          Read16(buffer + 8) != 0)
+        return CONTAINER_GIF;
+      break;
+    case TAG('I','M','A','_'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kIssSignature,
+                       sizeof(kIssSignature) - 1))
+        return CONTAINER_ISS;
+      break;
+    case TAG('k','!','\x00','\x40'):
+    case TAG('k','!','\x00','\x50'):
+      return CONTAINER_BIT;
+    case TAG('L','E','I','T'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kLxfSignature,
+                       sizeof(kLxfSignature) - 1))
+        return CONTAINER_LXF;
+      break;
+    case TAG('L','P','F',' '):
+      if (buffer_size > 24 &&
+          Read32(buffer + 16) == TAG('A','N','I','M') &&
+          Read16(buffer + 20) != 0 &&
+          Read16(buffer + 22) != 0)
+        return CONTAINER_ANM;
+      break;
+    case TAG('L','V','F','F'):
+      return CONTAINER_LVF;
+    case TAG('M','A','C',' '):
+      return CONTAINER_APE;
+    case TAG('M','M','M','D'):
+      if (third4 == TAG('C','N','T','I'))
+        return CONTAINER_MMF;
+      break;
+    case TAG('M','O','V','I'):
+      if (Read16(buffer + 4) < 3)
+        return CONTAINER_MV;
+      break;
+    case TAG('M','P','+','\x07'):
+    case TAG('M','P','+','\x17'):
+      return CONTAINER_MPC;
+    case TAG('M','P','C','K'):
+      if (check_mpc8(buffer, buffer_size))
+        return CONTAINER_MPC8;
+      break;
+    case TAG('N','I','S','T'):
+      if (second4 == TAG('_','1','A','\x0a'))
+        return CONTAINER_NISTSPHERE;
+      break;
+    case TAG('N','M','\x7a','\x56'):
+      if (second4 == TAG('\x1F','\x5F','\x04','\xAD'))
+        return CONTAINER_NUT;
+      break;
+    case TAG('N','S','V','f'):
+    case TAG('N','S','V','s'):
+      return CONTAINER_NSV;
+    case TAG('n','u','t','/'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kLibnutSignature,
+                       sizeof(kLibnutSignature) - 1))
+        return CONTAINER_LIBNUT;
+      break;
+    case TAG('N','u','p','p'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kNuv1Signature,
+                       sizeof(kNuv1Signature) - 1))
+        return CONTAINER_NUV;
+      break;
+    case TAG('M','y','t','h'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kNuv2Signature,
+                       sizeof(kNuv2Signature) - 1))
+        return CONTAINER_NUV;
+      break;
+    case TAG('O','N','2',' '):
+      if (third4 == TAG('O','N','2','f'))
+        return CONTAINER_AVI;
+    case TAG('O','g','g','S'):
+      if (buffer[5] <= 7)
+        return CONTAINER_OGG;
+      break;
+    case TAG('P','a','c','k'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kPafSignature,
+                       sizeof(kPafSignature) - 1))
+        return CONTAINER_PAF;
+      break;
+    case TAG('p','m','p','m'):
+      if (Read32(buffer + 4) == 1)
+        return CONTAINER_PMP;
+      break;
+    case TAG('P','V','F','1'):
+      if (buffer[4] == '\n')
+        return CONTAINER_PVF;
+      break;
+    case TAG('R','F','6','4'):
+      if (buffer_size > 16 && Read32(buffer + 12) == TAG('d','s','6','4'))
+        return CONTAINER_WAV;
+      break;
+    case TAG('r','i','f','f'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kW64Signature,
+                       sizeof(kW64Signature) - 1) &&
+          CompareEqual(buffer + 24,
+                       buffer_size - 24,
+                       kW64Signature2,
+                       sizeof(kW64Signature2) - 1))
+        return CONTAINER_W64;
+      break;
+    case TAG('R','I','F','F'):
+      switch (third4) {
+        case TAG('4','X','M','V'):
+          return CONTAINER_4XM;
+        case TAG('A','V','I',' '):
+        case TAG('A','V','I','X'):
+        case TAG('A','V','I','\x19'):
+        case TAG('A','M','V',' '):
+          return CONTAINER_AVI;
+        case TAG('Q','L','C','M'):
+          if (buffer_size > 16 && Read32(buffer + 12) == TAG('f','m','t',' '))
+            return CONTAINER_QCP;
+          break;
+        case TAG('W','A','V','E'):
+          // possibly ACT or WAV
+          return (check_act(buffer, buffer_size)) ?
+            CONTAINER_ACT : CONTAINER_WAV;
+        case TAG('X','W','M','A'):
+          return CONTAINER_XWMA;
+      }
+      break;
+    case TAG('R','S','T','M'):
+      next = Read16(buffer + 4);
+      if (next == 0xfffe || next == 0xfeff)
+        return CONTAINER_BRSTM;
+      break;
+    case TAG('S','A','N','M'):
+      if (third4 == TAG('S','H','D','R'))
+        return CONTAINER_SMUSH;
+      break;
+    case TAG('S','I','F','F'):
+      if (third4 == TAG('V','B','V','1') || third4 == TAG('S','O','U','N'))
+        return CONTAINER_SIFF;
+      break;
+    case TAG('S','M','K','2'):
+    case TAG('S','M','K','4'):
+      return CONTAINER_SMK;
+    case TAG('S','T','R','M'):
+      if (buffer_size > 18 && Read16(buffer + 10) && Read16(buffer + 12) &&
+          Read16(buffer + 16))
+        return CONTAINER_AST;
+      break;
+    case TAG('t','B','a','K'):
+      return CONTAINER_TAK;
+    case TAG('T','H','P','\x00'):
+      return CONTAINER_THP;
+    case TAG('T','M','A','V'):
+      if (check_tmv(buffer, buffer_size))
+        return CONTAINER_TMV;
+      break;
+    case TAG('T','T','A','1'):
+      return CONTAINER_TTA;
+    case TAG('\x55','\xaa','\x00','\x00'):
+      if (check_dsicin(buffer, buffer_size))
+        return CONTAINER_DSICIN;
+      break;
+    case TAG('T','W','I','N'):
+      if (check_vqf(buffer, buffer_size))
+        return CONTAINER_VQF;
+      break;
+    case TAG('V','I','D','\x00'):
+      return CONTAINER_BETHSOFTVID;
+    case TAG('w','W','\x10','\x00'):
+      return CONTAINER_AVS;
+    case TAG('w','v','p','k'):
+      return CONTAINER_WV;
+    case TAG('X','A','\x00','\x00'):
+    case TAG('X','A','I','\x00'):
+    case TAG('X','A','J','\x00'):
+      if (check_xa(buffer, buffer_size))
+        return CONTAINER_XA;
+      break;
+    case TAG('X','B','I','N'):
+      if (check_xbin(buffer, buffer_size))
+        return CONTAINER_XBIN;
+      break;
+    case TAG('Y','U','V','4'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kYuv4Signature,
+                       sizeof(kYuv4Signature) - 1))
+        return CONTAINER_YUV4MPEGPIPE;
+      break;
+    case TAG('W','E','B','V'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kWebvttSignature,
+                       sizeof(kWebvttSignature) - 1))
+        return CONTAINER_WEBVTT;
+      break;
+    case TAG('\xef','\xbb','\xbf','W'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kWebvttBomSignature,
+                       sizeof(kWebvttBomSignature) - 1))
+        return CONTAINER_WEBVTT;
+      break;
+    case TAG('[','S','c','r'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kAssSignature,
+                       sizeof(kAssSignature) - 1))
+        return CONTAINER_ASS;
+      break;
+    case TAG('\xef','\xbb','\xbf','['):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kAssBomSignature,
+                       sizeof(kAssBomSignature) - 1))
+        return CONTAINER_ASS;
+      break;
+    case TAG('<','w','i','n'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kRealSignature,
+                       sizeof(kRealSignature) - 1))
+        return CONTAINER_REALTEXT;
+      break;
+    case TAG('<','S','A','M'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kSamiSignature,
+                       sizeof(kSamiSignature) - 1))
+        return CONTAINER_SAMI;
+      break;
+    case TAG('\xef','\xbb','\xbf','<'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kRealBomSignature,
+                       sizeof(kRealBomSignature) - 1))
+        return CONTAINER_REALTEXT;
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kSamiBomSignature,
+                       sizeof(kSamiBomSignature) - 1))
+        return CONTAINER_SAMI;
+      break;
+    case TAG('\xb7','\xd8','\x00','\x20'):
+      if (CompareEqual(buffer,
+                       buffer_size,
+                       kWtvSignature,
+                       sizeof(kWtvSignature) - 1))
+        return CONTAINER_WTV;
+      break;
+  }
+
+  // Now try a few different ones that look at something other
+  // than the first 4 bytes
+  uint32_t first3 = first4 & 0xffffff00;
+  switch (first3) {
+    case TAG('A','M','V',0):
+      if (check_mtv(buffer, buffer_size))
+        return CONTAINER_MTV;
+      break;
+    case TAG('C','W','S',0):
+    case TAG('F','W','S',0):
+      return CONTAINER_SWF;
+    case TAG('F','R','M',0):
+      if (Read16(buffer + 4) != 0 && Read16(buffer + 6) != 0)
+        return CONTAINER_FRM;
+      break;
+    case TAG('A','V','\x01',0):
+    case TAG('A','V','\x02',0):
+      if (check_pva(buffer, buffer_size))
+        return CONTAINER_PVA;
+      break;
+    case TAG('I','D','3',0):
+      if (check_mp3(buffer, buffer_size, true))
+        return CONTAINER_MP3;
+      break;
+  }
+
+  // Maybe the first 2 characters are something we can use.
+  uint32_t first2 = first4 & 0xffff0000;
+  switch (first2) {
+    case 0x032e0000:
+      if (check_vmd(buffer, buffer_size))
+        return CONTAINER_VMD;
+      break;
+    case 0x04000000:
+    case 0x04040000:
+    case 0x040c0000:
+    case 0x04140000:
+      return CONTAINER_EA_CDATA;
+    case TAG('J','V',0,0):
+      if (CompareEqual(buffer + 4,
+                       buffer_size - 4,
+                       kJvSignature,
+                       sizeof(kJvSignature) - 1))
+        return CONTAINER_JV;
+      break;
+    case 0x0b770000:
+      if (check_ac3(buffer, buffer_size))
+        return CONTAINER_AC3;
+      if (check_eac3(buffer, buffer_size))
+        return CONTAINER_EAC3;
+      break;
+    case TAG('Y','O',0,0):
+      if (check_yop(buffer, buffer_size))
+        return CONTAINER_JV;
+      break;
+    case 0xfff00000:
+    case 0xfff10000:
+    case 0xfff80000:
+    case 0xfff90000:
+      if (check_aac(buffer, buffer_size))
+        return CONTAINER_AAC;
+      break;
+  }
+
+  // Now try the second set of 4 characters.
+  switch (second4) {
+    case 4:
+      if (buffer_size > 24 && buffer[3] == 0xc5 && Read32(buffer + 20) == 0xc)
+        return CONTAINER_VC1TEST;
+      break;
+    case TAG('R','E','D','1'):
+      return CONTAINER_R3D;
+  }
+
+  switch (Read16(buffer + 4)) {
+    case 0xaf11:
+    case 0xaf12:
+    case 0xaf13:
+      if (buffer_size > 20 &&
+          third4 <= 4096 &&
+          Read16(buffer + 10) <= 4096 &&
+          (Read16(buffer + 16) == 0xf1fa || Read32(buffer + 16) <= 2000))
+        return CONTAINER_FLIC;
+      break;
+  }
+
+  // Lastly, there are some that are other simple checks but don't fit
+  // the above case statements.
+  if (check_c93(buffer, buffer_size))
+    return CONTAINER_C93;
+  if (check_cdxl(buffer, buffer_size))
+    return CONTAINER_CDXL;
+  if (check_idcin(buffer, buffer_size))
+    return CONTAINER_IDCIN;
+  if (check_loas(buffer, buffer_size))
+    return CONTAINER_LOAS;
+  if (check_m4v(buffer, buffer_size))
+    return CONTAINER_M4V;
+  if (check_mov(buffer, buffer_size))
+    return CONTAINER_MOV;
+  if (check_vivo(buffer, buffer_size))
+    return CONTAINER_VIVO;
+  if (check_wsaud(buffer, buffer_size))
+    return CONTAINER_WSAUD;
+  if (check_xmv(buffer, buffer_size))
+    return CONTAINER_XMV;
+  // Check if the file is in MP3 format without the header
+  if (check_mp3(buffer, buffer_size, false))
+    return CONTAINER_MP3;
+
+  // skip over starting 0's, and see if it is MP3/AC3/EAC3
+  if (buffer[0] == 0) {
+    size_t offset = 1;
+    size_t remaining = buffer_size - 1;
+    while (remaining > 0 && buffer[offset] == 0) {
+      ++offset;
+      --remaining;
+    }
+    if (remaining > 32) {
+      // not worth trying if only a small number of bytes left
+      if (Read16(buffer + offset) == 0x0b77) {
+        if (check_ac3(buffer + offset, remaining))
+          return CONTAINER_AC3;
+        if (check_eac3(buffer + offset, remaining))
+          return CONTAINER_EAC3;
+      }
+      else if (check_mp3(buffer + offset, remaining, false))
+        return CONTAINER_MP3;
+    }
+  }
+
+  return CONTAINER_UNKNOWN;
+}
+
+static const char ipm_string[] = "Interplay MVE File\x1A\0\x1A";
+static const char mxf_string[] =
+    "\x06\x0e\x2b\x34\x02\x05\x01\x01\x0d\x01\x02\x01\x01\x02";
+static const char sub1_string[] = "******** START SCRIPT ********";
+
+// Attempt to determine the container type by scanning for a set of strings,
+// character by character. It covers the following containers:
+//   ipmovie, mxf, subviewer1
+static FFmpegContainerName LookupContainerByStringScan(const uint8 buffer[],
+                                                       size_t buffer_size) {
+  size_t offset = 0;
+  size_t remaining = buffer_size;
+  while (offset + 4 < buffer_size) {
+    uint32_t tag = Read32(buffer + offset);
+    switch (tag) {
+      case TAG('I','n','t','e'):
+        if (CompareEqual(buffer + offset,
+                         remaining,
+                         ipm_string,
+                         sizeof(ipm_string) - 1))
+          return CONTAINER_IPMOVIE;
+        break;
+      case 0x060e2b34:
+        if (CompareEqual(buffer + offset,
+                         remaining,
+                         mxf_string,
+                         sizeof(mxf_string) - 1))
+          return CONTAINER_MXF;
+        break;
+      case TAG('*','*','*','*'):
+        if (CompareEqual(buffer + offset,
+                         remaining,
+                         sub1_string,
+                         sizeof(sub1_string) - 1))
+          return CONTAINER_SUBVIEWER1;
+        break;
+      case TAG('N','S','V','s'):
+        if (check_nsv(buffer + offset, remaining))
+          return CONTAINER_NSV;
+        break;
+      case 0x001800a0:
+      case 0x00180140:
+        if (check_msnwctcp(buffer + offset, remaining))
+          return CONTAINER_MSNWCTCP;
+        break;
+    }
+
+    // Not found, move forward to next character.
+    ++offset;
+    --remaining;
+  }
+
+  // didn't find a string match for any of the formats
+  return CONTAINER_UNKNOWN;
+}
+
+// Helper function to do limited scanf functionality without going off
+// the end of the buffer.
+static bool SaferScanf(const uint8_t* buffer,
+                       size_t buffer_size,
+                       const char* format) {
+  // This function only supports the following items in the format string:
+  //   %<maxlength>d   -- integer (can start with +/-, maxlength is optional)
+  //   %<maxlength>u   -- unsigned integer (only digits, maxlength is optional)
+  //   %c              -- any single character
+  //   %[<characters>] -- character must be one of the set
+  //                   -- everything else is a literal
+  // This code assumes that format is correct.
+  size_t offset = 0;
+  while (offset < buffer_size) {
+    // Determine next format item.
+    if (*format == '\0') {
+      // End of format string, success.
+      return true;
+    } else if (*format != '%') {
+      // Not a specifier, so it must match exactly
+      if (buffer[offset] != *format)
+        return false;
+      ++offset;
+    } else {
+      ++format;
+      int maxLength = 0;
+      int numSeen = 0;
+      while (isdigit(*format)) {
+        maxLength = maxLength * 10 + (*format - '0');
+        ++format;
+      }
+      if (maxLength < 1)  // If not specified set it to 100 to simplify below
+        maxLength = 100;
+      switch (*format) {
+        case 'c':
+          ++offset;  // Don't care what the character is
+          break;
+        case 'd':
+          if (buffer[offset] == '+' || buffer[offset] == '-')
+            ++offset;
+        case 'u':
+          // need to process up to maxLength digits
+          while (offset < buffer_size &&
+                 --maxLength >= 0 &&
+                 isdigit(buffer[offset])) {
+            ++numSeen;
+            ++offset;
+          }
+          if (numSeen == 0)  // No digits, so it is not a match for %d/%u
+            return false;
+          break;
+        case '[':
+          ++format;  // Skip [
+          while (*format != ']') {
+            if (buffer[offset] == *format) {
+              ++numSeen;
+            }
+            ++format;
+          }
+          if (numSeen == 0)  // No character match
+            return false;
+          ++offset;  // Skip the character matched
+          break;
+        default:
+          NOTREACHED();
+      }
+    }
+    // Move to the next format specification.
+    ++format;
+  }
+  // Out of buffer, so it doesn't match
+  return false;
+}
+
+// Attempt to determine the container type by scanning for a set of strings,
+// line by line. It covers the following containers:
+//   microdvd, mpl2, mpsub, pjs, sdp, srt, subviewer, vplayer
+static FFmpegContainerName LookupContainerByStringLine(const uint8 buffer[],
+                                                       size_t buffer_size) {
+  size_t offset = CompareEqual(buffer, buffer_size, BYTE_ORDER_MARK, 3) ? 3 : 0;
+  size_t lines = 0;
+
+  // PJS is a scan from the beginning only.
+  if (SaferScanf(buffer, buffer_size, "%d,%d,%c"))
+    if (check_pjs(buffer, buffer_size))
+      return CONTAINER_PJS;
+
+  // Same for VPLAYER.
+  if (SaferScanf(buffer, buffer_size, "%d:%d:%d.%d%[: =]"))
+    return CONTAINER_VPLAYER;
+
+  // Same for AQTITLE
+  if (SaferScanf(buffer, buffer_size, "-->> %d"))
+    return CONTAINER_AQTITLE;
+
+  while (offset < buffer_size) {
+    const uint8_t* ptr = buffer + offset;
+    size_t remaining = buffer_size - offset;;
+
+    if (*ptr == '{' && lines < 3) {
+      if (SaferScanf(ptr, remaining, "{%d}{}%c") ||
+          SaferScanf(ptr, remaining, "{%d}{%d}%c") ||
+          SaferScanf(ptr, remaining, "{DEFAULT}{}%c"))
+        return CONTAINER_MICRODVD;
+    }
+
+    if (*ptr == '[' && lines < 3) {
+      if (SaferScanf(ptr, remaining, "[%64d][%64d]%c") ||
+          SaferScanf(ptr, remaining, "[%64d][]%c"))
+        return CONTAINER_MPL2;
+    }
+
+    if (*ptr == 'F') {
+      if (SaferScanf(ptr, remaining, "FORMAT=%d") ||
+          SaferScanf(ptr, remaining, "FORMAT=TIME"))
+        return CONTAINER_MPSUB;
+    }
+
+    if (*ptr == 'c') {
+      if (CompareEqual(ptr, remaining, "c=IN IP", 7))
+        return CONTAINER_SDP;
+    }
+
+    if (isdigit(*ptr) && lines < 3) {
+      if (SaferScanf(
+              ptr, remaining, "%d:%2d:%2d%[,.]%3d --> %d:%2d:%2d%[,.]%3d"))
+        return CONTAINER_SRT;
+    }
+
+    if (isdigit(*ptr) && lines < 1) {
+      if (SaferScanf(ptr, remaining, "%u:%u:%u.%u,%u:%u:%u.%u%c") ||
+          CompareEqual(ptr, remaining, "[INFORMATION]", 13))
+        return CONTAINER_SUBVIEWER;
+    }
+
+    // Find the end of the line.
+    while (buffer[offset] != '\n' && buffer[offset] != '\r' &&
+           offset < buffer_size)
+      ++offset;
+
+    // Skip the \n\r.
+    while ((buffer[offset] == '\n' || buffer[offset] == '\r') &&
+           offset < buffer_size)
+      ++offset;
+    ++lines;
+  }
+
+  // Didn't find a string match for any of the formats.
+  return CONTAINER_UNKNOWN;
+}
+
+// The strings in the list below are the ones returned by FFmpeg.
+// This would be the string from AVInputFormat.name. The list is
+// sorted by string alphabetically, so that we can use a binary
+// search when looking for a container by name.
+const ContainerNameMapping ContainerNames::container_name_mapping[] = {
+  { CONTAINER_4XM,          "4xm" },
+  { CONTAINER_AAC,          "aac" },
+  { CONTAINER_AC3,          "ac3" },
+  { CONTAINER_ACT,          "act" },
+  { CONTAINER_ADF,          "adf" },
+  { CONTAINER_ADX,          "adx" },
+  { CONTAINER_AEA,          "aea" },
+  { CONTAINER_AFC,          "afc" },
+  { CONTAINER_AIFF,         "aiff" },
+  { CONTAINER_ALAW,         "alaw" },
+  { CONTAINER_ALSA,         "alsa" },
+  { CONTAINER_AMR,          "amr" },
+  { CONTAINER_ANM,          "anm" },
+  { CONTAINER_APC,          "apc" },
+  { CONTAINER_APE,          "ape" },
+  { CONTAINER_AQTITLE,      "aqtitle" },
+  { CONTAINER_ASF,          "asf" },
+  { CONTAINER_ASS,          "ass" },
+  { CONTAINER_AST,          "ast" },
+  { CONTAINER_AU,           "au" },
+  { CONTAINER_AVI,          "avi" },
+  { CONTAINER_AVISYNTH,     "avisynth" },
+  { CONTAINER_AVR,          "avr" },
+  { CONTAINER_AVS,          "avs" },
+  { CONTAINER_BETHSOFTVID,  "bethsoftvid" },
+  { CONTAINER_BFI,          "bfi" },
+  { CONTAINER_BIN,          "bin" },
+  { CONTAINER_BINK,         "bink" },
+  { CONTAINER_BIT,          "bit" },
+  { CONTAINER_BKTR,         "bktr" },
+  { CONTAINER_BMV,          "bmv" },
+  { CONTAINER_BRSTM,        "brstm" },
+  { CONTAINER_C93,          "c93" },
+  { CONTAINER_CAF,          "caf" },
+  { CONTAINER_CAVSVIDEO,    "cavsvideo" },
+  { CONTAINER_CDG,          "cdg" },
+  { CONTAINER_CDXL,         "cdxl" },
+  { CONTAINER_CONCAT,       "concat" },
+  { CONTAINER_DAUD,         "daud" },
+  { CONTAINER_DFA,          "dfa" },
+  { CONTAINER_DIRAC,        "dirac" },
+  { CONTAINER_DNXHD,        "dnxhd" },
+  { CONTAINER_DSHOW,        "dshow" },
+  { CONTAINER_DSICIN,       "dsicin" },
+  { CONTAINER_DTS,          "dts" },
+  { CONTAINER_DTSHD,        "dtshd" },
+  { CONTAINER_DV,           "dv" },
+  { CONTAINER_DV1394,       "dv1394" },
+  { CONTAINER_DXA,          "dxa" },
+  { CONTAINER_EA,           "ea" },
+  { CONTAINER_EA_CDATA,     "ea_cdata" },
+  { CONTAINER_EAC3,         "eac3" },
+  { CONTAINER_EPAF,         "epaf" },
+  { CONTAINER_F32BE,        "f32be" },
+  { CONTAINER_F32LE,        "f32le" },
+  { CONTAINER_F64BE,        "f64be" },
+  { CONTAINER_F64LE,        "f64le" },
+  { CONTAINER_FBDEV,        "fbdev" },
+  { CONTAINER_FFM,          "ffm" },
+  { CONTAINER_FFMETADATA,   "ffmetadata" },
+  { CONTAINER_FILM_CPK,     "film_cpk" },
+  { CONTAINER_FILMSTRIP,    "filmstrip" },
+  { CONTAINER_FLAC,         "flac" },
+  { CONTAINER_FLIC,         "flic" },
+  { CONTAINER_FLV,          "flv" },
+  { CONTAINER_FRM,          "frm" },
+  { CONTAINER_G722,         "g722" },
+  { CONTAINER_G723_1,       "g723_1" },
+  { CONTAINER_G729,         "g729" },
+  { CONTAINER_GIF,          "gif" },
+  { CONTAINER_GSM,          "gsm" },
+  { CONTAINER_GXF,          "gxf" },
+  { CONTAINER_H261,         "h261" },
+  { CONTAINER_H263,         "h263" },
+  { CONTAINER_H264,         "h264" },
+  { CONTAINER_HLS,          "hls,applehttp" },
+  { CONTAINER_ICO,          "ico" },
+  { CONTAINER_IDCIN,        "idcin" },
+  { CONTAINER_IDF,          "idf" },
+  { CONTAINER_IEC61883,     "iec61883" },
+  { CONTAINER_IFF,          "iff" },
+  { CONTAINER_ILBC,         "ilbc" },
+  { CONTAINER_IMAGE2,       "image2" },
+  { CONTAINER_IMAGE2PIPE,   "image2pipe" },
+  { CONTAINER_INGENIENT,    "ingenient" },
+  { CONTAINER_IPMOVIE,      "ipmovie" },
+  { CONTAINER_IRCAM,        "ircam" },
+  { CONTAINER_ISS,          "iss" },
+  { CONTAINER_IV8,          "iv8" },
+  { CONTAINER_IVF,          "ivf" },
+  { CONTAINER_JACK,         "jack" },
+  { CONTAINER_JACOSUB,      "jacosub" },
+  { CONTAINER_JV,           "jv" },
+  { CONTAINER_LATM,         "latm" },
+  { CONTAINER_LAVFI,        "lavfi" },
+  { CONTAINER_LIBCDIO,      "libcdio" },
+  { CONTAINER_LIBDC1394,    "libdc1394" },
+  { CONTAINER_LIBMODPLUG,   "libmodplug" },
+  { CONTAINER_LIBNUT,       "libnut" },
+  { CONTAINER_LMLM4,        "lmlm4" },
+  { CONTAINER_LOAS,         "loas" },
+  { CONTAINER_LVF,          "lvf" },
+  { CONTAINER_LXF,          "lxf" },
+  { CONTAINER_M4V,          "m4v" },
+  { CONTAINER_WEBM,         "matroska,webm" },
+  { CONTAINER_MGSTS,        "mgsts" },
+  { CONTAINER_MICRODVD,     "microdvd" },
+  { CONTAINER_MJPEG,        "mjpeg" },
+  { CONTAINER_MLP,          "mlp" },
+  { CONTAINER_MM,           "mm" },
+  { CONTAINER_MMF,          "mmf" },
+  { CONTAINER_MOV,          "mov,mp4,m4a,3gp,3g2,mj2" },
+  { CONTAINER_MP3,          "mp3" },
+  { CONTAINER_MPC,          "mpc" },
+  { CONTAINER_MPC8,         "mpc8" },
+  { CONTAINER_MPEG,         "mpeg" },
+  { CONTAINER_MPEGTS,       "mpegts" },
+  { CONTAINER_MPEGTSRAW,    "mpegtsraw" },
+  { CONTAINER_MPEGVIDEO,    "mpegvideo" },
+  { CONTAINER_MPL2,         "mpl2" },
+  { CONTAINER_MPSUB,        "mpsub" },
+  { CONTAINER_MSNWCTCP,     "msnwctcp" },
+  { CONTAINER_MTV,          "mtv" },
+  { CONTAINER_MULAW,        "mulaw" },
+  { CONTAINER_MV,           "mv" },
+  { CONTAINER_MVI,          "mvi" },
+  { CONTAINER_MXF,          "mxf" },
+  { CONTAINER_MXG,          "mxg" },
+  { CONTAINER_NC,           "nc" },
+  { CONTAINER_NISTSPHERE,   "nistsphere" },
+  { CONTAINER_NSV,          "nsv" },
+  { CONTAINER_NUT,          "nut" },
+  { CONTAINER_NUV,          "nuv" },
+  { CONTAINER_OGG,          "ogg" },
+  { CONTAINER_OMA,          "oma" },
+  { CONTAINER_OPENAL,       "openal" },
+  { CONTAINER_OSS,          "oss" },
+  { CONTAINER_PAF,          "paf" },
+  { CONTAINER_PJS,          "pjs" },
+  { CONTAINER_PMP,          "pmp" },
+  { CONTAINER_PSXSTR,       "psxstr" },
+  { CONTAINER_PULSE,        "pulse" },
+  { CONTAINER_PVA,          "pva" },
+  { CONTAINER_PVF,          "pvf" },
+  { CONTAINER_QCP,          "qcp" },
+  { CONTAINER_R3D,          "r3d" },
+  { CONTAINER_RAWVIDEO,     "rawvideo" },
+  { CONTAINER_RDT,          "rdt" },
+  { CONTAINER_REALTEXT,     "realtext" },
+  { CONTAINER_RL2,          "rl2" },
+  { CONTAINER_RM,           "rm" },
+  { CONTAINER_ROQ,          "roq" },
+  { CONTAINER_RPL,          "rpl" },
+  { CONTAINER_RSO,          "rso" },
+  { CONTAINER_RTP,          "rtp" },
+  { CONTAINER_RTSP,         "rtsp" },
+  { CONTAINER_S16BE,        "s16be" },
+  { CONTAINER_S16LE,        "s16le" },
+  { CONTAINER_S24BE,        "s24be" },
+  { CONTAINER_S24LE,        "s24le" },
+  { CONTAINER_S32BE,        "s32be" },
+  { CONTAINER_S32LE,        "s32le" },
+  { CONTAINER_S8,           "s8" },
+  { CONTAINER_SAMI,         "sami" },
+  { CONTAINER_SAP,          "sap" },
+  { CONTAINER_SBG,          "sbg" },
+  { CONTAINER_SDP,          "sdp" },
+  { CONTAINER_SHN,          "shn" },
+  { CONTAINER_SIFF,         "siff" },
+  { CONTAINER_SMJPEG,       "smjpeg" },
+  { CONTAINER_SMK,          "smk" },
+  { CONTAINER_SMUSH,        "smush" },
+  { CONTAINER_SNDIO,        "sndio" },
+  { CONTAINER_SOL,          "sol" },
+  { CONTAINER_SOX,          "sox" },
+  { CONTAINER_SPDIF,        "spdif" },
+  { CONTAINER_SRT,          "srt" },
+  { CONTAINER_SUBVIEWER,    "subviewer" },
+  { CONTAINER_SUBVIEWER1,   "subviewer1" },
+  { CONTAINER_SWF,          "swf" },
+  { CONTAINER_TAK,          "tak" },
+  { CONTAINER_TEDCAPTIONS,  "tedcaptions" },
+  { CONTAINER_THP,          "thp" },
+  { CONTAINER_TIERTEXSEQ,   "tiertexseq" },
+  { CONTAINER_TMV,          "tmv" },
+  { CONTAINER_TRUEHD,       "truehd" },
+  { CONTAINER_TTA,          "tta" },
+  { CONTAINER_TTY,          "tty" },
+  { CONTAINER_TXD,          "txd" },
+  { CONTAINER_VC1,          "vc1" },
+  { CONTAINER_VC1TEST,      "vc1test" },
+  { CONTAINER_VFWCAP,       "vfwcap" },
+  { CONTAINER_V4L,          "video4linux,v4l" },
+  { CONTAINER_V4L2,         "video4linux2,v4l2" },
+  { CONTAINER_VIVO,         "vivo" },
+  { CONTAINER_VMD,          "vmd" },
+  { CONTAINER_VOBSUB,       "vobsub" },
+  { CONTAINER_VOC,          "voc" },
+  { CONTAINER_VPLAYER,      "vplayer" },
+  { CONTAINER_VQF,          "vqf" },
+  { CONTAINER_W64,          "w64" },
+  { CONTAINER_WAV,          "wav" },
+  { CONTAINER_WC3MOVIE,     "wc3movie" },
+  { CONTAINER_WEBVTT,       "webvtt" },
+  { CONTAINER_WSAUD,        "wsaud" },
+  { CONTAINER_WSVQA,        "wsvqa" },
+  { CONTAINER_WTV,          "wtv" },
+  { CONTAINER_WV,           "wv" },
+  { CONTAINER_X11GRAB,      "x11grab" },
+  { CONTAINER_XA,           "xa" },
+  { CONTAINER_XBIN,         "xbin" },
+  { CONTAINER_XMV,          "xmv" },
+  { CONTAINER_XWMA,         "xwma" },
+  { CONTAINER_YOP,          "yop" },
+  { CONTAINER_YUV4MPEGPIPE, "yuv4mpegpipe" }
+};
+
+// Returns the number of elements in container_name_mapping.
+const int ContainerNames::ContainerNameMappingSize() {
+  return arraysize(container_name_mapping);
+}
+
+// Lookup a container name using the list above (container_name_mapping)
+// to determine the container enum. If not found (recent addition to
+// FFmpeg or a name change), return CONTAINER_UNKNOWN.
+FFmpegContainerName ContainerNames::LookupContainer(
+    const char* container_name) {
+  DCHECK(container_name);
+  const ContainerNameMapping* found =
+      std::lower_bound(container_name_mapping,
+                       container_name_mapping + ContainerNameMappingSize() - 1,
+                       container_name,
+                       ContainerNameMappingComparer);
+  return (strcasecmp(found->name, container_name) == 0) ? found->id
+                                                        : CONTAINER_UNKNOWN;
+}
+
+// Attempt to determine the container name from the buffer provided.
+FFmpegContainerName ContainerNames::DetermineContainer(const uint8 buffer[],
+                                                       size_t buffer_size) {
+  // TODO(jrummell): The following formats are not scanned for
+  //    cavsvideo, dts, dv, h261, h263, h264, jacosub,
+  //    mpeg, mpegts, mpegvideo, psxstr, sbg, spdif, tedcaptions
+
+  // First attempt the simple checks, that typically look at just the
+  // first few bytes of the file.
+  FFmpegContainerName result = LookupContainerByFirst4(buffer, buffer_size);
+  if (result != CONTAINER_UNKNOWN)
+    return result;
+
+  // No success with simple test, so attempt to determine the container by
+  // looking for strings in the buffer.
+  result = LookupContainerByStringScan(buffer, buffer_size);
+  if (result != CONTAINER_UNKNOWN)
+    return result;
+  return LookupContainerByStringLine(buffer, buffer_size);
+}
+
+// Log the container based on the name returned by FFmpeg.
+void ContainerNames::LogContainer(const char* container_name) {
+  FFmpegContainerName container = LookupContainer(container_name);
+  LogContainerToHistogram(container, false);
+}
+
+// Log the container by examining the first part of the stream.
+void ContainerNames::LogContainer(const uint8 buffer[], size_t buffer_size) {
+  FFmpegContainerName container = DetermineContainer(buffer, buffer_size);
+  LogContainerToHistogram(container, true);
+}
+
+}  // namespace media