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 251fbdfabf440b52f65fb6b36c3fc6cf7317e1e3..ab2de16e1f80edb410cb57c529b393470a7e7a5f 100644
--- a/media/ffmpeg/ffmpeg_common.cc
+++ b/media/ffmpeg/ffmpeg_common.cc
@@ -327,6 +327,16 @@ bool AVCodecContextToAudioDecoderConfig(
   ChannelLayout channel_layout = ChannelLayoutToChromeChannelLayout(
       codec_context->channel_layout, codec_context->channels);
 
+  // If it is an Opus channel mapping with discrete channels, or there are more
+  // channels than supported in the renderer, use CHANNEL_LAYOUT_DISCRETE.
+  bool is_opus_discrete = false;
+  if (codec == kCodecOpus && codec_context->extradata_size >= 19) {
+    int mapping_family = codec_context->extradata[18];
+    is_opus_discrete = mapping_family == 2;
+  }
+  if (is_opus_discrete || channel_layout == CHANNEL_LAYOUT_UNSUPPORTED)

[DaleCurtis, 2017/03/29 22:46:55]

Do we need this || clause? Seems like we might allow playback of unexpected
things (potentially leading to security issues).

[flim-chromium, 2017/03/30 19:35:10]

Sorry, I misunderstood your original comment. Fixed now.

+    channel_layout = CHANNEL_LAYOUT_DISCRETE;
+
   int sample_rate = codec_context->sample_rate;
   switch (codec) {
     // For AC3/EAC3 we enable only demuxing, but not decoding, so FFmpeg does
@@ -371,6 +381,7 @@ bool AVCodecContextToAudioDecoderConfig(
   config->Initialize(codec, sample_format, channel_layout, sample_rate,
                      extra_data, encryption_scheme, seek_preroll,
                      codec_context->delay);
+  config->SetChannelsForDiscrete(codec_context->channels);
 
 #if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
   // These are bitstream formats unknown to ffmpeg, so they don't have
@@ -419,8 +430,7 @@ 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()) {