Fixing AudioBuffer params and channel layout bugs

media/filters/ffmpeg_audio_decoder.cc

Index: media/filters/ffmpeg_audio_decoder.cc
diff --git a/media/filters/ffmpeg_audio_decoder.cc b/media/filters/ffmpeg_audio_decoder.cc
index b5dc7177655e033adc51c583d9035b08b2667b7d..be839bb14a6efd7887c900cbea5dcd2a696ae2de 100644
--- a/media/filters/ffmpeg_audio_decoder.cc
+++ b/media/filters/ffmpeg_audio_decoder.cc
@@ -300,10 +300,18 @@ bool FFmpegAudioDecoder::FFmpegDecode(
       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 &&
@@ -322,7 +330,8 @@ bool FFmpegAudioDecoder::FFmpegDecode(
                              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!"