--- a/content/media/AudioNodeStream.h
+++ b/content/media/AudioNodeStream.h
@@ -103,16 +103,22 @@ public:
   bool IsAudioParamStream() const
   {
     return mAudioParamStream;
   }
   const OutputChunks& LastChunks() const
   {
     return mLastChunks;
   }
+  virtual bool MainThreadNeedsUpdates() const MOZ_OVERRIDE
+  {
+    // Only source and external streams need updates on the main thread.
+    return (mKind == MediaStreamGraph::SOURCE_STREAM && mFinished) ||
+           mKind == MediaStreamGraph::EXTERNAL_STREAM;
+  }
 
   // Any thread
   AudioNodeEngine* Engine() { return mEngine; }
   TrackRate SampleRate() const { return mSampleRate; }
 
 protected:
   void FinishOutput();
 

--- a/content/media/MediaStreamGraph.cpp
+++ b/content/media/MediaStreamGraph.cpp
@@ -890,16 +890,19 @@ MediaStreamGraphImpl::PlayVideo(MediaStr
 
 void
 MediaStreamGraphImpl::PrepareUpdatesToMainThreadState(bool aFinalUpdate)
 {
   mMonitor.AssertCurrentThreadOwns();
 
   for (uint32_t i = 0; i < mStreams.Length(); ++i) {
     MediaStream* stream = mStreams[i];
+    if (!stream->MainThreadNeedsUpdates()) {
+      continue;
+    }
     StreamUpdate* update = mStreamUpdates.AppendElement();
     update->mGraphUpdateIndex = stream->mGraphUpdateIndices.GetAt(mCurrentTime);
     update->mStream = stream;
     update->mNextMainThreadCurrentTime =
       GraphTimeToStreamTime(stream, mCurrentTime);
     update->mNextMainThreadFinished =
       stream->mFinished &&
       StreamTimeToGraphTime(stream, stream->GetBufferEnd()) <= mCurrentTime;

--- a/content/media/MediaStreamGraph.h
+++ b/content/media/MediaStreamGraph.h
@@ -438,16 +438,22 @@ public:
   void ApplyTrackDisabling(TrackID aTrackID, MediaSegment* aSegment);
 
   DOMMediaStream* GetWrapper()
   {
     NS_ASSERTION(NS_IsMainThread(), "Only use DOMMediaStream on main thread");
     return mWrapper;
   }
 
+  // Return true if the main thread needs to observe updates from this stream.
+  virtual bool MainThreadNeedsUpdates() const
+  {
+    return true;
+  }
+
 protected:
   virtual void AdvanceTimeVaryingValuesToCurrentTime(GraphTime aCurrentTime, GraphTime aBlockedTime)
   {
     mBufferStartTime += aBlockedTime;
     mGraphUpdateIndices.InsertTimeAtStart(aBlockedTime);
     mGraphUpdateIndices.AdvanceCurrentTime(aCurrentTime);
     mExplicitBlockerCount.AdvanceCurrentTime(aCurrentTime);
 
@@ -932,17 +938,17 @@ public:
    * tracks, whichever is greater.
    * TODO at some point we will probably need to add API to select
    * particular tracks of each input stream.
    */
   ProcessedMediaStream* CreateTrackUnionStream(DOMMediaStream* aWrapper);
   // Internal AudioNodeStreams can only pass their output to another
   // AudioNode, whereas external AudioNodeStreams can pass their output
   // to an nsAudioStream for playback.
-  enum AudioNodeStreamKind { INTERNAL_STREAM, EXTERNAL_STREAM };
+  enum AudioNodeStreamKind { SOURCE_STREAM, INTERNAL_STREAM, EXTERNAL_STREAM };
   /**
    * Create a stream that will process audio for an AudioNode.
    * Takes ownership of aEngine.  aSampleRate is the sampling rate used
    * for the stream.  If 0 is passed, the sampling rate of the engine's
    * node will get used.
    */
   AudioNodeStream* CreateAudioNodeStream(AudioNodeEngine* aEngine,
                                          AudioNodeStreamKind aKind,

--- a/content/media/webaudio/AudioBufferSourceNode.cpp
+++ b/content/media/webaudio/AudioBufferSourceNode.cpp
@@ -433,17 +433,17 @@ AudioBufferSourceNode::AudioBufferSource
   , mDuration(std::numeric_limits<double>::min())
   , mPlaybackRate(new AudioParam(this, SendPlaybackRateToStream, 1.0f))
   , mLoop(false)
   , mStartCalled(false)
   , mStopped(false)
 {
   mStream = aContext->Graph()->CreateAudioNodeStream(
       new AudioBufferSourceNodeEngine(this, aContext->Destination()),
-      MediaStreamGraph::INTERNAL_STREAM);
+      MediaStreamGraph::SOURCE_STREAM);
   mStream->AddMainThreadListener(this);
 }
 
 AudioBufferSourceNode::~AudioBufferSourceNode()
 {
   if (Context()) {
     Context()->UnregisterAudioBufferSourceNode(this);
   }