Re-add AC3/EAC3 audio demuxing support

media/formats/mp4/mp4_stream_parser.cc

Index: media/formats/mp4/mp4_stream_parser.cc
diff --git a/media/formats/mp4/mp4_stream_parser.cc b/media/formats/mp4/mp4_stream_parser.cc
index af64343b6237d21e5b7654febc418b36cadaa2f2..c1102f4f031e67d72496111055be3136e8605803 100644
--- a/media/formats/mp4/mp4_stream_parser.cc
+++ b/media/formats/mp4/mp4_stream_parser.cc
@@ -217,9 +217,16 @@ bool MP4StreamParser::ParseMoov(BoxReader* reader) {
       const AudioSampleEntry& entry = samp_descr.audio_entries[desc_idx];
       const AAC& aac = entry.esds.aac;
 
-      if (!(entry.format == FOURCC_MP4A ||
-            (entry.format == FOURCC_ENCA &&
-             entry.sinf.format.format == FOURCC_MP4A))) {
+      FourCC audio_format = (entry.format == FOURCC_ENCA)

[ddorwin, 2016/01/04 23:22:17]

If you can provide some context on this (basically, why ENCA is different), that
would be great.

[servolk, 2016/01/07 02:30:04]

FOURCC_ENCA just means that audio stream is encrypted and actual format is in
entry.sinf.format.format. Added a comment.

+                                ? entry.sinf.format.format
+                                : entry.format;

[ddorwin, 2016/01/04 23:22:17]

nit: Empty line after since this is it's own chunk of logic and separate from
the following block.

[servolk, 2016/01/07 02:30:04]

Done.

+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+      if (audio_format != FOURCC_MP4A && audio_format != FOURCC_A52 &&

[ddorwin, 2016/01/04 23:22:17]

I think a switch statement will be cleaner and avoid code duplication.

[servolk, 2016/01/07 02:30:04]

Now that I've removed a52/a52b the ifs are only four lines and fairly readable,
switch would be more verbose than that.

+          audio_format != FOURCC_A52b && audio_format != FOURCC_AC3 &&

[ddorwin, 2016/01/04 23:22:17]

I see AC3 and EAC3 values are mixed here. Should they be kept together?

[servolk, 2016/01/07 02:30:04]

Now, with only one value for AC3/EAC3 each, this looks cleaner.

+          audio_format != FOURCC_AC_3 && audio_format != FOURCC_EAC3) {
+#else
+      if (audio_format != FOURCC_MP4A) {
+#endif
         MEDIA_LOG(ERROR, media_log_) << "Unsupported audio format 0x"
                                      << std::hex << entry.format
                                      << " in stsd box.";
@@ -227,6 +234,17 @@ bool MP4StreamParser::ParseMoov(BoxReader* reader) {
       }
 
       uint8_t audio_type = entry.esds.object_type;
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+      if (audio_type == kForbidden &&

[ddorwin, 2016/01/04 23:22:17]

No need to duplicate the kForbidden check. Put everything else inside the if
block. Can you explain what kFobidden means in this case?

[servolk, 2016/01/07 02:30:04]

kForbidden means the mp4 parser used by MSE doesn't recognize this format and
that's fine, since we only need to be able to demux it to implement audio
pass-through.

+          (audio_format == FOURCC_EAC3 || audio_format == FOURCC_A52b)) {

[ddorwin, 2016/01/04 23:22:17]

With the change above, a switch statement probably makes sense.

[servolk, 2016/01/07 02:30:04]

Now that we have only two values, I believe if should be cleaner.

+        audio_type = kEAC3;
+      }
+      if (audio_type == kForbidden &&
+          (audio_format == FOURCC_A52 || audio_format == FOURCC_AC3 ||

[ddorwin, 2016/01/04 23:22:17]

AC3 has been before EAC3 except here.

[servolk, 2016/01/07 02:30:04]

Fixed the ordering above. AC3 should be before EAC3.

+           audio_format == FOURCC_AC_3)) {
+        audio_type = kAC3;
+      }
+#endif
       DVLOG(1) << "audio_type " << std::hex << static_cast<int>(audio_type);
       if (audio_object_types_.find(audio_type) == audio_object_types_.end()) {
         MEDIA_LOG(ERROR, media_log_)
@@ -249,6 +267,16 @@ bool MP4StreamParser::ParseMoov(BoxReader* reader) {
 #if defined(OS_ANDROID)
         extra_data = aac.codec_specific_data();
 #endif
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+      } else if (audio_type == kAC3) {
+        codec = kCodecAC3;
+        channel_layout = GuessChannelLayout(entry.channelcount);
+        sample_per_second = entry.samplerate;
+      } else if (audio_type == kEAC3) {
+        codec = kCodecEAC3;
+        channel_layout = GuessChannelLayout(entry.channelcount);
+        sample_per_second = entry.samplerate;
+#endif
       } else {
         MEDIA_LOG(ERROR, media_log_) << "Unsupported audio object type 0x"
                                      << std::hex << audio_type << " in esds.";