Re-add AC3/EAC3 audio demuxing support

media/formats/mp4/mp4_stream_parser.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/formats/mp4/mp4_stream_parser.h"
 
 #include <limits>
 #include <vector>
 
 #include "base/callback_helpers.h"
@@ skipping 199 matching lines @@
     if (track->media.handler.type == kAudio && !audio_config.IsValidConfig()) {
       RCHECK(!samp_descr.audio_entries.empty());
 
       // It is not uncommon to find otherwise-valid files with incorrect sample
       // description indices, so we fail gracefully in that case.
       if (desc_idx >= samp_descr.audio_entries.size())
         desc_idx = 0;
       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.";
         return false;
       }
 
       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_)
             << "audio object type 0x" << std::hex << audio_type
             << " does not match what is specified in the"
             << " mimetype.";
         return false;
       }
 
       AudioCodec codec = kUnknownAudioCodec;
       ChannelLayout channel_layout = CHANNEL_LAYOUT_NONE;
       int sample_per_second = 0;
       std::vector<uint8_t> extra_data;
       // Check if it is MPEG4 AAC defined in ISO 14496 Part 3 or
       // supported MPEG2 AAC varients.
       if (ESDescriptor::IsAAC(audio_type)) {
         codec = kCodecAAC;
         channel_layout = aac.GetChannelLayout(has_sbr_);
         sample_per_second = aac.GetOutputSamplesPerSecond(has_sbr_);
 #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.";
         return false;
       }
 
       SampleFormat sample_format;
       if (entry.samplesize == 8) {
         sample_format = kSampleFormatU8;
       } else if (entry.samplesize == 16) {
@@ skipping 362 matching lines @@
       runs.AdvanceSample();
     }
     runs.AdvanceRun();
   }
 
   return true;
 }
 
 }  // namespace mp4
 }  // namespace media