Bug 901633 - Part 13 - Teach the resampler at the input of the MSG to dynamically change its channel count if needed. r=jesup

When the audio comes from a PeerConnection, we don't know how many channels the
audio will have, and it can change anyways.

--HG--
extra : rebase_source : b4d78217db012d2d94ede6d6724209b6046fbb29

dom/media/MediaStreamGraph.cpp

@@ -2483,24 +2483,19 @@ SourceMediaStream::ResampleAudioToGraphSampleRate(TrackData* aTrackData, MediaSe
   AudioSegment* segment = static_cast<AudioSegment*>(aSegment);
   int channels = segment->ChannelCount();
 
-  // If this segment is just silence, we delay instanciating the resampler.
-  if (channels) {
-    if (aTrackData->mResampler) {
-      MOZ_ASSERT(aTrackData->mResamplerChannelCount == segment->ChannelCount());
-    } else {
-      SpeexResamplerState* state = speex_resampler_init(channels,
-                                                        aTrackData->mInputRate,
-                                                        GraphImpl()->GraphRate(),
-                                                        SPEEX_RESAMPLER_QUALITY_MIN,
-                                                        nullptr);
-      if (!state) {
-        return;
-      }
-      aTrackData->mResampler.own(state);
-#ifdef DEBUG
-      aTrackData->mResamplerChannelCount = channels;
-#endif
+  // If this segment is just silence, we delay instanciating the resampler. We
+  // also need to recreate the resampler if the channel count changes.
+  if (channels && aTrackData->mResamplerChannelCount != channels) {
+    SpeexResamplerState* state = speex_resampler_init(channels,
+        aTrackData->mInputRate,
+        GraphImpl()->GraphRate(),
+        SPEEX_RESAMPLER_QUALITY_MIN,
+        nullptr);
+    if (!state) {
+      return;
     }
+    aTrackData->mResampler.own(state);
+    aTrackData->mResamplerChannelCount = channels;
   }
   segment->ResampleChunks(aTrackData->mResampler, aTrackData->mInputRate, GraphImpl()->GraphRate());
 }

dom/media/MediaStreamGraph.h

@@ -897,9 +897,7 @@ protected:
     // Resampler if the rate of the input track does not match the
     // MediaStreamGraph's.
     nsAutoRef<SpeexResamplerState> mResampler;
-#ifdef DEBUG
     int mResamplerChannelCount;
-#endif
     StreamTime mStart;
     // End-time of data already flushed to the track (excluding mData)
     StreamTime mEndOfFlushedData;