Bug 1112445 - Ignore the audio stream when determining whether we should skip-t-o-next-keyframe for async readers. r=mattwoodrow

dom/media/MediaDecoderReader.h

@@ -243,6 +243,12 @@ public:
     mDecoder = nullptr;
   }
 
+  // Returns true if the reader implements RequestAudioData()
+  // and RequestVideoData() asynchronously, rather than using the
+  // implementation in this class to adapt the old synchronous to
+  // the newer async model.
+  virtual bool IsAsync() const { return false; }
+
 protected:
   virtual ~MediaDecoderReader();
 

dom/media/MediaDecoderStateMachine.cpp

@@ -612,15 +612,20 @@ MediaDecoderStateMachine::NeedToSkipToNextKeyframe()
   // data to decode. If we're running low on downloaded data to decode,
   // we won't start keyframe skipping, as we'll be pausing playback to buffer
   // soon anyway and we'll want to be able to display frames immediately
-  // after buffering finishes.
-  bool isLowOnDecodedAudio = !mIsAudioPrerolling && IsAudioDecoding() &&
+  // after buffering finishes. We ignore the low audio calculations for
+  // readers that are async, as since their audio decode runs on a different
+  // task queue it should never run low and skipping won't help their decode.
+  bool isLowOnDecodedAudio = !mReader->IsAsync() &&
+                             !mIsAudioPrerolling && IsAudioDecoding() &&
                              (GetDecodedAudioDuration() <
                               mLowAudioThresholdUsecs * mPlaybackRate);
   bool isLowOnDecodedVideo = !mIsVideoPrerolling &&
                              (mDecodedVideoEndTime - GetClock() <
                               LOW_VIDEO_THRESHOLD_USECS * mPlaybackRate);
-  if ((isLowOnDecodedAudio || isLowOnDecodedVideo) && !HasLowUndecodedData()) {
-    DECODER_LOG("Skipping video decode to the next keyframe");
+  bool lowUndecoded = HasLowUndecodedData();
+  if ((isLowOnDecodedAudio || isLowOnDecodedVideo) && !lowUndecoded) {
+    DECODER_LOG("Skipping video decode to the next keyframe lowAudio=%d lowVideo=%d lowUndecoded=%d async=%d",
+                isLowOnDecodedAudio, isLowOnDecodedVideo, lowUndecoded, mReader->IsAsync());
     return true;
   }
 
@@ -994,10 +999,14 @@ MediaDecoderStateMachine::OnVideoDecoded(VideoData* aVideoSample)
         StopPrerollingVideo();
       }
 
-      // If the requested video sample was slow to arrive, increase the
-      // amount of audio we buffer to ensure that we don't run out of audio.
-      // TODO: Detect when we're truly async, and don't do this if so, as
-      // it's not necessary.
+      // For non async readers, if the requested video sample was slow to
+      // arrive, increase the amount of audio we buffer to ensure that we
+      // don't run out of audio. This is unnecessary for async readers,
+      // since they decode audio and video on different threads so they
+      // are unlikely to run out of decoded audio.
+      if (mReader->IsAsync()) {
+        return;
+      }
       TimeDuration decodeTime = TimeStamp::Now() - mVideoDecodeStartTime;
       if (THRESHOLD_FACTOR * DurationToUsecs(decodeTime) > mLowAudioThresholdUsecs &&
           !HasLowUndecodedData())

dom/media/fmp4/MP4Reader.h

@@ -82,6 +82,8 @@ public:
 
   virtual nsRefPtr<ShutdownPromise> Shutdown() MOZ_OVERRIDE;
 
+  virtual bool IsAsync() const MOZ_OVERRIDE { return true; }
+
 private:
 
   bool InitDemuxer();

dom/media/mediasource/MediaSourceReader.h

@@ -130,6 +130,11 @@ public:
   nsresult SetCDMProxy(CDMProxy* aProxy);
 #endif
 
+  virtual bool IsAsync() const MOZ_OVERRIDE {
+    return (!mAudioReader || mAudioReader->IsAsync()) &&
+           (!mVideoReader || mVideoReader->IsAsync());
+  }
+
 private:
   // Switch the current audio/video reader to the reader that
   // contains aTarget (or up to aError after target). Both

dom/media/omx/MediaCodecReader.h

@@ -110,6 +110,8 @@ public:
 
   virtual android::sp<android::MediaSource> GetAudioOffloadTrack();
 
+  virtual bool IsAsync() const MOZ_OVERRIDE { return true; }
+
 protected:
   struct TrackInputCopier
   {