diff --git a/packager/media/base/audio_stream_info.cc b/packager/media/base/audio_stream_info.cc
index 45e04b7ca6..39adcad273 100644
--- a/packager/media/base/audio_stream_info.cc
+++ b/packager/media/base/audio_stream_info.cc
@@ -19,42 +19,24 @@ std::string AudioCodecToString(AudioCodec audio_codec) {
   switch (audio_codec) {
     case kCodecAAC:
       return "AAC";
-    case kCodecMP3:
-      return "MP3";
-    case kCodecPCM:
-      return "PCM";
-    case kCodecVorbis:
-      return "Vorbis";
-    case kCodecFLAC:
-      return "FLAC";
-    case kCodecAMR_NB:
-      return "AMR_NB";
-    case kCodecAMR_WB:
-      return "AMR_WB";
-    case kCodecPCM_MULAW:
-      return "PCM_MULAW";
-    case kCodecGSM_MS:
-      return "GSM_MS";
-    case kCodecPCM_S16BE:
-      return "PCM_S16BE";
-    case kCodecPCM_S24BE:
-      return "PCM_S24BE";
-    case kCodecOpus:
-      return "Opus";
-    case kCodecEAC3:
-      return "EAC3";
+    case kCodecAC3:
+      return "AC3";
     case kCodecDTSC:
       return "DTSC";
+    case kCodecDTSE:
+      return "DTSE";
     case kCodecDTSH:
       return "DTSH";
     case kCodecDTSL:
       return "DTSL";
-    case kCodecDTSE:
-      return "DTSE";
-    case kCodecDTSP:
-      return "DTS+";
     case kCodecDTSM:
       return "DTS-";
+    case kCodecDTSP:
+      return "DTS+";
+    case kCodecOpus:
+      return "Opus";
+    case kCodecVorbis:
+      return "Vorbis";
     default:
       NOTIMPLEMENTED() << "Unknown Audio Codec: " << audio_codec;
       return "UnknownAudioCodec";
@@ -131,6 +113,8 @@ std::string AudioStreamInfo::GetCodecString(AudioCodec codec,
       return "dts+";
     case kCodecDTSM:
       return "dts-";
+    case kCodecAC3:
+      return "ac-3";
     default:
       NOTIMPLEMENTED() << "Codec: " << codec;
       return "unknown";
diff --git a/packager/media/base/audio_stream_info.h b/packager/media/base/audio_stream_info.h
index 6cad7dc997..dd11c7d342 100644
--- a/packager/media/base/audio_stream_info.h
+++ b/packager/media/base/audio_stream_info.h
@@ -17,24 +17,15 @@ namespace media {
 enum AudioCodec {
   kUnknownAudioCodec = 0,
   kCodecAAC,
-  kCodecMP3,
-  kCodecPCM,
-  kCodecVorbis,
-  kCodecFLAC,
-  kCodecAMR_NB,
-  kCodecAMR_WB,
-  kCodecPCM_MULAW,
-  kCodecGSM_MS,
-  kCodecPCM_S16BE,
-  kCodecPCM_S24BE,
-  kCodecOpus,
-  kCodecEAC3,
+  kCodecAC3,
   kCodecDTSC,
+  kCodecDTSE,
   kCodecDTSH,
   kCodecDTSL,
-  kCodecDTSE,
-  kCodecDTSP,
   kCodecDTSM,
+  kCodecDTSP,
+  kCodecOpus,
+  kCodecVorbis,
 
   kNumAudioCodec
 };
diff --git a/packager/media/formats/mp4/box_definitions.cc b/packager/media/formats/mp4/box_definitions.cc
index f05e790aa1..062117ffd6 100644
--- a/packager/media/formats/mp4/box_definitions.cc
+++ b/packager/media/formats/mp4/box_definitions.cc
@@ -134,7 +134,8 @@ bool FileType::ReadWriteInternal(BoxBuffer* buffer) {
          buffer->ReadWriteUInt32(&minor_version));
   size_t num_brands;
   if (buffer->Reading()) {
-    num_brands = (buffer->Size() - buffer->Pos()) / sizeof(FourCC);
+    RCHECK(buffer->BytesLeft() % sizeof(FourCC) == 0);
+    num_brands = buffer->BytesLeft() / sizeof(FourCC);
     compatible_brands.resize(num_brands);
   } else {
     num_brands = compatible_brands.size();
@@ -318,8 +319,8 @@ bool SampleEncryption::ReadWriteInternal(BoxBuffer* buffer) {
   // If we don't know |iv_size|, store sample encryption data to parse later
   // after we know iv_size.
   if (buffer->Reading() && iv_size == 0) {
-    RCHECK(buffer->ReadWriteVector(&sample_encryption_data,
-                                   buffer->Size() - buffer->Pos()));
+    RCHECK(
+        buffer->ReadWriteVector(&sample_encryption_data, buffer->BytesLeft()));
     return true;
   }
 
@@ -1395,7 +1396,7 @@ bool DTSSpecific::ReadWriteInternal(BoxBuffer* buffer) {
          buffer->ReadWriteUInt8(&pcm_sample_depth));
 
   if (buffer->Reading()) {
-    RCHECK(buffer->ReadWriteVector(&extra_data, buffer->Size() - buffer->Pos()));
+    RCHECK(buffer->ReadWriteVector(&extra_data, buffer->BytesLeft()));
   } else {
     if (extra_data.empty()) {
       extra_data.assign(kDdtsExtraData,
@@ -1415,6 +1416,25 @@ uint32_t DTSSpecific::ComputeSizeInternal() {
          sizeof(kDdtsExtraData);
 }
 
+AC3Specific::AC3Specific() {}
+AC3Specific::~AC3Specific() {}
+
+FourCC AC3Specific::BoxType() const { return FOURCC_DAC3; }
+
+bool AC3Specific::ReadWriteInternal(BoxBuffer* buffer) {
+  RCHECK(ReadWriteHeaderInternal(buffer) &&
+         buffer->ReadWriteVector(
+             &data, buffer->Reading() ? buffer->BytesLeft() : data.size()));
+  return true;
+}
+
+uint32_t AC3Specific::ComputeSizeInternal() {
+  // This box is optional. Skip it if not initialized.
+  if (data.empty())
+    return 0;
+  return HeaderSize() + data.size();
+}
+
 AudioSampleEntry::AudioSampleEntry()
     : format(FOURCC_NULL),
       data_reference_index(1),
@@ -1468,15 +1488,16 @@ bool AudioSampleEntry::ReadWriteInternal(BoxBuffer* buffer) {
 
   RCHECK(buffer->TryReadWriteChild(&esds));
   RCHECK(buffer->TryReadWriteChild(&ddts));
+  RCHECK(buffer->TryReadWriteChild(&dac3));
   return true;
 }
 
 uint32_t AudioSampleEntry::ComputeSizeInternal() {
   return HeaderSize() + sizeof(data_reference_index) + sizeof(channelcount) +
          sizeof(samplesize) + sizeof(samplerate) + sinf.ComputeSize() +
-         esds.ComputeSize() + ddts.ComputeSize() + 6 +
-         8 +  // 6 + 8 bytes reserved.
-         4;   // 4 bytes predefined.
+         esds.ComputeSize() + ddts.ComputeSize() + dac3.ComputeSize() +
+         6 + 8 +  // 6 + 8 bytes reserved.
+         4;       // 4 bytes predefined.
 }
 
 WebVTTConfigurationBox::WebVTTConfigurationBox() {}
@@ -1623,7 +1644,7 @@ FourCC DataEntryUrl::BoxType() const { return FOURCC_URL; }
 bool DataEntryUrl::ReadWriteInternal(BoxBuffer* buffer) {
   RCHECK(ReadWriteHeaderInternal(buffer));
   if (buffer->Reading()) {
-    RCHECK(buffer->ReadWriteVector(&location, buffer->Size() - buffer->Pos()));
+    RCHECK(buffer->ReadWriteVector(&location, buffer->BytesLeft()));
   } else {
     RCHECK(buffer->ReadWriteVector(&location, location.size()));
   }
diff --git a/packager/media/formats/mp4/box_definitions.h b/packager/media/formats/mp4/box_definitions.h
index 1cd56df23e..12ff1f5a7d 100644
--- a/packager/media/formats/mp4/box_definitions.h
+++ b/packager/media/formats/mp4/box_definitions.h
@@ -309,6 +309,12 @@ struct DTSSpecific : Box {
   std::vector<uint8_t> extra_data;
 };
 
+struct AC3Specific : Box {
+  DECLARE_BOX_METHODS(AC3Specific);
+
+  std::vector<uint8_t> data;
+};
+
 struct AudioSampleEntry : Box {
   DECLARE_BOX_METHODS(AudioSampleEntry);
   // Returns actual format of this sample entry.
@@ -325,6 +331,7 @@ struct AudioSampleEntry : Box {
   ProtectionSchemeInfo sinf;
   ElementaryStreamDescriptor esds;
   DTSSpecific ddts;
+  AC3Specific dac3;
 };
 
 struct WebVTTConfigurationBox : Box {
diff --git a/packager/media/formats/mp4/box_definitions_comparison.h b/packager/media/formats/mp4/box_definitions_comparison.h
index 6ba02840fb..896ad2b9e4 100644
--- a/packager/media/formats/mp4/box_definitions_comparison.h
+++ b/packager/media/formats/mp4/box_definitions_comparison.h
@@ -240,14 +240,19 @@ inline bool operator==(const DTSSpecific& lhs,
          lhs.extra_data == rhs.extra_data;
 }
 
+inline bool operator==(const AC3Specific& lhs,
+                       const AC3Specific& rhs) {
+  return lhs.data == rhs.data;
+}
+
 inline bool operator==(const AudioSampleEntry& lhs,
                        const AudioSampleEntry& rhs) {
   return lhs.format == rhs.format &&
          lhs.data_reference_index == rhs.data_reference_index &&
          lhs.channelcount == rhs.channelcount &&
          lhs.samplesize == rhs.samplesize && lhs.samplerate == rhs.samplerate &&
-         lhs.sinf == rhs.sinf && lhs.esds == rhs.esds &&
-         lhs.ddts == rhs.ddts;
+         lhs.sinf == rhs.sinf && lhs.esds == rhs.esds && lhs.ddts == rhs.ddts &&
+         lhs.dac3 == rhs.dac3;
 }
 
 inline bool operator==(const WebVTTConfigurationBox& lhs,
diff --git a/packager/media/formats/mp4/box_definitions_unittest.cc b/packager/media/formats/mp4/box_definitions_unittest.cc
index 06e79bbe67..7d83ba4e3c 100644
--- a/packager/media/formats/mp4/box_definitions_unittest.cc
+++ b/packager/media/formats/mp4/box_definitions_unittest.cc
@@ -380,6 +380,16 @@ class BoxDefinitionsTestGeneral : public testing::Test {
     ddts->pcm_sample_depth = 24;
   }
 
+  void Fill(AC3Specific* dac3) {
+    const uint8_t kAc3Data[] = {0x50, 0x11, 0x60};
+    dac3->data.assign(kAc3Data, kAc3Data + arraysize(kAc3Data));
+  }
+
+  void Modify(AC3Specific* dac3) {
+    const uint8_t kAc3Data[] = {0x50, 0x11, 0x40};
+    dac3->data.assign(kAc3Data, kAc3Data + arraysize(kAc3Data));
+  }
+
   void Fill(AudioSampleEntry* enca) {
     enca->format = FOURCC_ENCA;
     enca->data_reference_index = 2;
@@ -884,6 +894,7 @@ class BoxDefinitionsTestGeneral : public testing::Test {
   bool IsOptional(const CodecConfigurationRecord* box) { return true; }
   bool IsOptional(const PixelAspectRatio* box) { return true; }
   bool IsOptional(const ElementaryStreamDescriptor* box) { return true; }
+  bool IsOptional(const AC3Specific* box) { return true; }
   // Recommended, but optional.
   bool IsOptional(const WebVTTSourceLabelBox* box) { return true; }
   bool IsOptional(const CompositionTimeToSample* box) { return true; }
@@ -926,6 +937,7 @@ typedef testing::Types<FileType,
                        VideoSampleEntry,
                        ElementaryStreamDescriptor,
                        DTSSpecific,
+                       AC3Specific,
                        AudioSampleEntry,
                        WebVTTConfigurationBox,
                        WebVTTSourceLabelBox,
@@ -1072,6 +1084,21 @@ TEST_F(BoxDefinitionsTest, DTSSampleEntry) {
   ASSERT_EQ(entry, entry_readback);
 }
 
+TEST_F(BoxDefinitionsTest, AC3SampleEntry) {
+  AudioSampleEntry entry;
+  entry.format = FOURCC_AC3;
+  entry.data_reference_index = 2;
+  entry.channelcount = 5;
+  entry.samplesize = 16;
+  entry.samplerate = 44100;
+  Fill(&entry.dac3);
+  entry.Write(this->buffer_.get());
+
+  AudioSampleEntry entry_readback;
+  ASSERT_TRUE(ReadBack(&entry_readback));
+  ASSERT_EQ(entry, entry_readback);
+}
+
 TEST_F(BoxDefinitionsTest, ProtectionSystemSpecificHeader) {
   ProtectionSystemSpecificHeader pssh;
   Fill(&pssh);
diff --git a/packager/media/formats/mp4/fourccs.h b/packager/media/formats/mp4/fourccs.h
index a070d9b817..19bfaf2532 100644
--- a/packager/media/formats/mp4/fourccs.h
+++ b/packager/media/formats/mp4/fourccs.h
@@ -16,12 +16,14 @@ enum FourCC {
   FOURCC_NULL = 0,
   FOURCC_ID32 = 0x49443332,
   FOURCC_PRIV = 0x50524956,
+  FOURCC_AC3 = 0x61632d33,  // This fourcc is "ac-3".
   FOURCC_AVC1 = 0x61766331,
   FOURCC_AVCC = 0x61766343,
   FOURCC_BLOC = 0x626C6F63,
   FOURCC_CENC = 0x63656e63,
   FOURCC_CO64 = 0x636f3634,
   FOURCC_CTTS = 0x63747473,
+  FOURCC_DAC3 = 0x64616333,
   FOURCC_DASH = 0x64617368,
   FOURCC_DDTS = 0x64647473,
   FOURCC_DINF = 0x64696e66,
@@ -32,7 +34,6 @@ enum FourCC {
   FOURCC_DTSL = 0x6474736c,
   FOURCC_DTSM = 0x6474732d,
   FOURCC_DTSP = 0x6474732b,
-  FOURCC_EAC3 = 0x65632d33,
   FOURCC_EDTS = 0x65647473,
   FOURCC_ELST = 0x656c7374,
   FOURCC_ENCA = 0x656e6361,
diff --git a/packager/media/formats/mp4/mp4_media_parser.cc b/packager/media/formats/mp4/mp4_media_parser.cc
index cf1b658b45..19e508c3f7 100644
--- a/packager/media/formats/mp4/mp4_media_parser.cc
+++ b/packager/media/formats/mp4/mp4_media_parser.cc
@@ -74,8 +74,8 @@ AudioCodec FourCCToAudioCodec(FourCC fourcc) {
       return kCodecDTSP;
     case FOURCC_DTSM:
       return kCodecDTSM;
-    case FOURCC_EAC3:
-      return kCodecEAC3;
+    case FOURCC_AC3:
+      return kCodecAC3;
     default:
       return kUnknownAudioCodec;
   }
@@ -410,7 +410,8 @@ bool MP4MediaParser::ParseMoov(BoxReader* reader) {
           num_channels = entry.channelcount;
           sampling_frequency = entry.samplerate;
           break;
-        case FOURCC_EAC3:
+        case FOURCC_AC3:
+          extra_data = entry.dac3.data;
           num_channels = entry.channelcount;
           sampling_frequency = entry.samplerate;
           break;
diff --git a/packager/media/formats/mp4/mp4_muxer.cc b/packager/media/formats/mp4/mp4_muxer.cc
index 52764393d2..e07ddd03b0 100644
--- a/packager/media/formats/mp4/mp4_muxer.cc
+++ b/packager/media/formats/mp4/mp4_muxer.cc
@@ -63,6 +63,8 @@ FourCC AudioCodecToFourCC(AudioCodec codec) {
   switch (codec) {
     case kCodecAAC:
       return FOURCC_MP4A;
+    case kCodecAC3:
+      return FOURCC_AC3;
     case kCodecDTSC:
       return FOURCC_DTSC;
     case kCodecDTSH:
@@ -261,6 +263,9 @@ void MP4Muxer::GenerateAudioTrak(const AudioStreamInfo* audio_info,
       audio.ddts.sampling_frequency = audio_info->sampling_frequency();
       audio.ddts.pcm_sample_depth = audio_info->sample_bits();
       break;
+    case kCodecAC3:
+      audio.dac3.data = audio_info->extra_data();
+      break;
     default:
       NOTIMPLEMENTED();
       break;