Re-add AC3/EAC3 audio demuxing support

media/filters/stream_parser_factory.cc

Index: media/filters/stream_parser_factory.cc
diff --git a/media/filters/stream_parser_factory.cc b/media/filters/stream_parser_factory.cc
index 23218bc1959e2cfd3a229a8ad36a975dc48553e1..d877f2880442bc8eb3d1ac9cf3382b8169be2a26 100644
--- a/media/filters/stream_parser_factory.cc
+++ b/media/filters/stream_parser_factory.cc
@@ -50,7 +50,8 @@ struct CodecInfo {
     HISTOGRAM_EAC3,
     HISTOGRAM_MP3,
     HISTOGRAM_OPUS,
-    HISTOGRAM_MAX = HISTOGRAM_OPUS  // Must be equal to largest logged entry.
+    HISTOGRAM_AC3,
+    HISTOGRAM_MAX = HISTOGRAM_AC3  // Must be equal to largest logged entry.
   };
 
   const char* pattern;
@@ -150,6 +151,21 @@ static const CodecInfo kMPEG4AACCodecInfo = { "mp4a.40.*", CodecInfo::AUDIO,
 static const CodecInfo kMPEG2AACLCCodecInfo = { "mp4a.67", CodecInfo::AUDIO,
                                                 NULL,
                                                 CodecInfo::HISTOGRAM_MPEG2AAC };
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+// The 'ac-3' and 'ec-3' are mime codec ids for AC3 and EAC3 according to
+// http://www.mp4ra.org/codecs.html
+// The object types for AC3 and EAC3 in MP4 container are 0xa5 and 0xa6, so
+// according to RFC 6381 this corresponds to codec ids 'mp4a.a5' and 'mp4a.a6'.
+// Different applications use different codec ids.
+static const CodecInfo kAC3CodecInfo1 =  { "ac-3", CodecInfo::AUDIO, NULL,
+                                          CodecInfo::HISTOGRAM_AC3 };
+static const CodecInfo kAC3CodecInfo2 =  { "mp4a.a5", CodecInfo::AUDIO, NULL,
+                                          CodecInfo::HISTOGRAM_AC3 };
+static const CodecInfo kEAC3CodecInfo1 = { "ec-3", CodecInfo::AUDIO, NULL,
+                                          CodecInfo::HISTOGRAM_EAC3 };
+static const CodecInfo kEAC3CodecInfo2 = { "mp4a.a6", CodecInfo::AUDIO, NULL,
+                                          CodecInfo::HISTOGRAM_EAC3 };
+#endif
 
 static const CodecInfo* kVideoMP4Codecs[] = {
   &kH264AVC1CodecInfo,
@@ -162,6 +178,12 @@ static const CodecInfo* kVideoMP4Codecs[] = {
 static const CodecInfo* kAudioMP4Codecs[] = {
   &kMPEG4AACCodecInfo,
   &kMPEG2AACLCCodecInfo,
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+  &kAC3CodecInfo1,
+  &kAC3CodecInfo2,
+  &kEAC3CodecInfo1,
+  &kEAC3CodecInfo2,
+#endif
   NULL
 };
 
@@ -185,6 +207,14 @@ static StreamParser* BuildMP4Parser(
         has_sbr = true;
         break;
       }
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    } else if (MatchPattern(codec_id, kAC3CodecInfo1.pattern) ||
+               MatchPattern(codec_id, kAC3CodecInfo2.pattern)) {
+      audio_object_types.insert(mp4::kAC3);
+    } else if (MatchPattern(codec_id, kEAC3CodecInfo1.pattern) ||
+               MatchPattern(codec_id, kEAC3CodecInfo2.pattern)) {
+      audio_object_types.insert(mp4::kEAC3);
+#endif
     }
   }