Bug 895730 - AudioTrackEncoder should handle the case where audio chunk is null. r=roc

content/media/encoder/TrackEncoder.cpp

@@ -16,7 +16,8 @@
 
 namespace mozilla {
 
-#define MAX_FRAMES_TO_DROP  48000
+static const int  DEFAULT_CHANNELS = 1;
+static const int  DEFAULT_SAMPLING_RATE = 16000;
 
 void
 AudioTrackEncoder::NotifyQueuedTrackChanges(MediaStreamGraph* aGraph,
@@ -34,16 +35,25 @@ AudioTrackEncoder::NotifyQueuedTrackChanges(MediaStreamGraph* aGraph,
     AudioSegment::ChunkIterator iter(*audio);
     while (!iter.IsEnded()) {
       AudioChunk chunk = *iter;
-      if (chunk.mBuffer) {
+
-        Init(chunk.mChannelData.Length(), aTrackRate);
+      // The number of channels is determined by the first non-null chunk, and
+      // thus the audio encoder is initialized at this time.
+      if (!chunk.IsNull()) {
+        nsresult rv = Init(chunk.mChannelData.Length(), aTrackRate);
+        if (NS_SUCCEEDED(rv)) {
           break;
         }
+      } else {
+        mSilentDuration += chunk.mDuration;
+      }
       iter.Next();
     }
   }
 
   // Append and consume this raw segment.
+  if (mInitialized) {
     AppendAudioSegment(audio);
+  }
 
   // The stream has stopped and reached the end of track.
   if (aTrackEvents == MediaStreamListener::TRACK_EVENT_ENDED) {
@@ -57,35 +67,42 @@ AudioTrackEncoder::NotifyRemoved(MediaStreamGraph* aGraph)
 {
   // In case that MediaEncoder does not receive a TRACK_EVENT_ENDED event.
   LOG("[AudioTrackEncoder]: NotifyRemoved.");
+
+  // If source audio chunks are completely silent till the end of encoding,
+  // initialize the encoder with default channel counts and sampling rate, and
+  // append this many null data to the segment of track encoder.
+  if (!mInitialized && mSilentDuration > 0) {
+    Init(DEFAULT_CHANNELS, DEFAULT_SAMPLING_RATE);
+    mRawSegment->AppendNullData(mSilentDuration);
+    mSilentDuration = 0;
+  }
   NotifyEndOfStream();
 }
 
 nsresult
 AudioTrackEncoder::AppendAudioSegment(MediaSegment* aSegment)
 {
-  // Drop the in-coming segment if buffer(mRawSegment) is overflow.
   ReentrantMonitorAutoEnter mon(mReentrantMonitor);
 
   AudioSegment* audio = static_cast<AudioSegment*>(aSegment);
   AudioSegment::ChunkIterator iter(*audio);
 
-  if (mRawSegment->GetDuration() < MAX_FRAMES_TO_DROP) {
+  // Append this many null data to our queued segment if there is a complete
+  // silence before the audio track encoder has initialized.
+  if (mSilentDuration > 0) {
+    mRawSegment->AppendNullData(mSilentDuration);
+    mSilentDuration = 0;
+  }
+
   while (!iter.IsEnded()) {
     AudioChunk chunk = *iter;
-      if (chunk.mBuffer) {
+    // Append and consume both non-null and null chunks.
     mRawSegment->AppendAndConsumeChunk(&chunk);
-      }
     iter.Next();
   }
   if (mRawSegment->GetDuration() >= GetPacketDuration()) {
     mReentrantMonitor.NotifyAll();
   }
-  }
-#ifdef DEBUG
-  else {
-    LOG("[AudioTrackEncoder]: A segment has dropped!");
-  }
-#endif
 
   return NS_OK;
 }

content/media/encoder/TrackEncoder.h

@@ -74,6 +74,7 @@ public:
     , mRawSegment(new AudioSegment())
     , mEndOfStream(false)
     , mCanceled(false)
+    , mSilentDuration(0)
   {}
 
   void NotifyQueuedTrackChanges(MediaStreamGraph* aGraph, TrackID aID,
@@ -176,6 +177,12 @@ protected:
    * mReentrantMonitor.
    */
   bool mCanceled;
+
+  /**
+   * The total duration of null chunks we have received from MediaStreamGraph
+   * before initializing the audio track encoder.
+   */
+  TrackTicks mSilentDuration;
 };
 
 class VideoTrackEncoder : public TrackEncoder