Fixing AudioBuffer params and channel layout bugs

media/filters/ffmpeg_audio_decoder.cc

 // Copyright (c) 2012 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/filters/ffmpeg_audio_decoder.h"
 
 #include <stdint.h>
 
 #include "base/callback_helpers.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 282 matching lines @@
     packet.data += result;
 
     scoped_refptr<AudioBuffer> output;
 
     bool config_changed = false;
     if (frame_decoded) {
       const int channels = DetermineChannels(av_frame_.get());
       ChannelLayout channel_layout = ChannelLayoutToChromeChannelLayout(
           codec_context_->channel_layout, codec_context_->channels);
 
-      if (av_frame_->sample_rate != config_.samples_per_second() ||
-          channel_layout != config_.channel_layout() ||
+      bool is_config_stale =
+          av_frame_->sample_rate != config_.samples_per_second() ||
           channels != ChannelLayoutToChannelCount(config_.channel_layout()) ||
-          av_frame_->format != av_sample_format_) {
+          av_frame_->format != av_sample_format_;
+
+      // Only consider channel layout changes for AAC.
+      // TODO(tguilbert, dalecurtis): Due to http://crbug.com/600538 we need to
+      // allow channel layout changes for the moment. See if ffmpeg is fixable.

[chcunningham, 2016/04/19 00:28:56]

Just to confirm my understanding, we initially have CHANNEL_LAYOUT_5_1, but then
a buffer comes in with CHANNEL_LAYOUT_5_1_BACK, and we believe this is a bug in
FFmpeg? I don't know the .wav format (MPEG PS?) well... I can't say whether a
channel layout should be possible. 

Can you share the .wav files from the bug with me? I'm not able to download from
pantheon for some reason. I'm wondering which of these layouts is expected (if
not both). Also wondering how far reaching this bug is. 

[tguilbert, 2016/04/19 18:17:56]

I do not know if this is a bug per-say in Ffmpeg. We seemed to have never taken
this as a guarantee before. We don't set the layout [0] and it is potentially
overwritten from what I understand [1].

This failure did not happen mid stream, but failed as soon as the file started
playing.

0:
https://code.google.com/p/chromium/codesearch#chromium/src/media/ffmpeg/ffmpe...
1:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/ffmpeg...

+      if (config_.codec() == kCodecAAC)
+        is_config_stale |= channel_layout != config_.channel_layout();
+
+      if (is_config_stale) {
         // Only allow midstream configuration changes for AAC. Sample format is
         // not expected to change between AAC profiles.
         if (config_.codec() == kCodecAAC &&
             av_frame_->format == av_sample_format_) {
           MEDIA_LOG(DEBUG, media_log_)
               << " Detected AAC midstream configuration change"
               << " PTS:" << buffer->timestamp().InMicroseconds()
               << " Sample Rate: " << av_frame_->sample_rate << " vs "
               << config_.samples_per_second()
               << ", ChannelLayout: " << channel_layout << " vs "
               << config_.channel_layout() << ", Channels: " << channels
               << " vs "
               << ChannelLayoutToChannelCount(config_.channel_layout());
           config_.Initialize(config_.codec(), config_.sample_format(),
                              channel_layout, av_frame_->sample_rate,
                              config_.extra_data(), config_.encryption_scheme(),
                              config_.seek_preroll(), config_.codec_delay());
           config_changed = true;
-          ResetTimestampState();
+          if (av_frame_->sample_rate != config_.samples_per_second())
+            ResetTimestampState();
         } else {
           MEDIA_LOG(ERROR, media_log_)
               << "Unsupported midstream configuration change!"
               << " Sample Rate: " << av_frame_->sample_rate << " vs "
               << config_.samples_per_second() << ", Channels: " << channels
               << " vs " << ChannelLayoutToChannelCount(config_.channel_layout())
               << ", Sample Format: " << av_frame_->format << " vs "
               << av_sample_format_;
           // This is an unrecoverable error, so bail out.
           av_frame_unref(av_frame_.get());
@@ skipping 84 matching lines @@
   return true;
 }
 
 void FFmpegAudioDecoder::ResetTimestampState() {
   discard_helper_.reset(new AudioDiscardHelper(config_.samples_per_second(),
                                                config_.codec_delay()));
   discard_helper_->Reset(config_.codec_delay());
 }
 
 }  // namespace media