Support Opus Ambisonics playback

media/ffmpeg/ffmpeg_common.cc

Index: media/ffmpeg/ffmpeg_common.cc
diff --git a/media/ffmpeg/ffmpeg_common.cc b/media/ffmpeg/ffmpeg_common.cc
index 91836b87ec573b89ff6e8c50d6ce7e31cf0add1d..41ec439d11db48bce5eac5f2b6e8d6bfdc605b63 100644
--- a/media/ffmpeg/ffmpeg_common.cc
+++ b/media/ffmpeg/ffmpeg_common.cc
@@ -324,8 +324,17 @@ bool AVCodecContextToAudioDecoderConfig(
   SampleFormat sample_format = AVSampleFormatToSampleFormat(
       codec_context->sample_fmt, codec_context->codec_id);
 
-  ChannelLayout channel_layout = ChannelLayoutToChromeChannelLayout(
-      codec_context->channel_layout, codec_context->channels);
+  // If it is an Opus Ambisonics file, always use CHANNEL_LAYOUT_DISCRETE
+  int is_opus_ambisonics = 0;

[DaleCurtis, 2017/03/20 17:38:58]

bool

[flim-chromium, 2017/03/22 06:20:51]

Also renamed to is_opus_discrete to remove focus from ambisonics since it may
also make sense to make other Opus channel mappings discrete (e.g. 255?)

[flim-chromium, 2017/03/22 06:20:51]

Done.

+  if (codec == kCodecOpus && codec_context->extradata_size >= 19) {
+    int mapping_family = codec_context->extradata[18];
+    is_opus_ambisonics = mapping_family == 2;
+  }
+  ChannelLayout channel_layout = is_opus_ambisonics
+                                 ? CHANNEL_LAYOUT_DISCRETE

[DaleCurtis, 2017/03/20 17:38:58]

This should also include channels > kMaxConcurrentChannels; otherwise an
existing layout should be mapped.

[flim-chromium, 2017/03/22 06:20:51]

Done. Refactored slightly to avoid having to redefine kMaxConcurrentChannels
here.  

+                                 : ChannelLayoutToChromeChannelLayout(
+                                       codec_context->channel_layout,
+                                       codec_context->channels);
 
   int sample_rate = codec_context->sample_rate;
   switch (codec) {
@@ -371,6 +380,7 @@ bool AVCodecContextToAudioDecoderConfig(
   config->Initialize(codec, sample_format, channel_layout, sample_rate,
                      extra_data, encryption_scheme, seek_preroll,
                      codec_context->delay);
+  config->set_channels_for_discrete(codec_context->channels);
 
 #if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
   // These are bitstream formats unknown to ffmpeg, so they don't have
@@ -419,8 +429,7 @@ void AudioDecoderConfigToAVCodecContext(const AudioDecoderConfig& config,
 
   // TODO(scherkus): should we set |channel_layout|? I'm not sure if FFmpeg uses
   // said information to decode.
-  codec_context->channels =
-      ChannelLayoutToChannelCount(config.channel_layout());
+  codec_context->channels = config.channels();
   codec_context->sample_rate = config.samples_per_second();
 
   if (config.extra_data().empty()) {