Bug 1316211. P4 - remove CheckSlowDecoding() and friends since IsAsync() now always returns true. r=gerald

MozReview-Commit-ID: 3dOa0aUQ0kM

--HG--
extra : rebase_source : 3091fc002b28bd9d2b45c330a45c437032c4cf18
extra : source : b6fe47f3e125097d8d5c6dd322c948b6c483980a

dom/media/MediaDecoderStateMachine.cpp

@@ -92,18 +92,10 @@ namespace detail {
 // time premium for compensating the seeking delay.
 static constexpr auto RESUME_VIDEO_PREMIUM = TimeUnit::FromMicroseconds(125000);
 
-// If audio queue has less than this much decoded audio, we won't risk
-// trying to decode the video, we'll skip decoding video up to the next
-// keyframe. We may increase this value for an individual decoder if we
-// encounter video frames which take a long time to decode.
-static constexpr auto LOW_AUDIO_THRESHOLD = TimeUnit::FromMicroseconds(300000);
-
 static const int64_t AMPLE_AUDIO_USECS = 2000000;
 
 // If more than this much decoded audio is queued, we'll hold off
-// decoding more audio. If we increase the low audio threshold (see
-// LOW_AUDIO_THRESHOLD above) we'll also increase this value to ensure it's not
-// less than the low audio threshold.
+// decoding more audio.
 static constexpr auto AMPLE_AUDIO_THRESHOLD = TimeUnit::FromMicroseconds(AMPLE_AUDIO_USECS);
 
 } // namespace detail
@@ -122,12 +114,6 @@ static constexpr auto LOW_VIDEO_THRESHOLD = TimeUnit::FromMicroseconds(60000);
 // Arbitrary "frame duration" when playing only audio.
 static const int AUDIO_DURATION_USECS = 40000;
 
-// If we increase our "low audio threshold" (see LOW_AUDIO_THRESHOLD above), we
-// use this as a factor in all our calculations. Increasing this will cause
-// us to be more likely to increase our low audio threshold, and to
-// increase it by more.
-static const int THRESHOLD_FACTOR = 2;
-
 namespace detail {
 
 // If we have less than this much buffered data available, we'll consider
@@ -731,7 +717,6 @@ public:
     mMaster->PushVideo(aVideo);
     DispatchDecodeTasksIfNeeded();
     MaybeStopPrerolling();
-    CheckSlowDecoding(aDecodeStart);
   }
 
   void HandleAudioCanceled() override
@@ -815,37 +800,6 @@ private:
   void EnsureVideoDecodeTaskQueued();
   void MaybeStartBuffering();
 
-  void CheckSlowDecoding(TimeStamp aDecodeStart)
-  {
-    // 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 (Reader()->IsAsync()) {
-      return;
-    }
-
-    TimeDuration decodeTime = TimeStamp::Now() - aDecodeStart;
-    auto adjusted = TimeUnit::FromTimeDuration(decodeTime * THRESHOLD_FACTOR);
-    if (adjusted > mMaster->mLowAudioThreshold
-        && !mMaster->HasLowBufferedData())
-    {
-      mMaster->mLowAudioThreshold = std::min(
-        adjusted, mMaster->mAmpleAudioThreshold);
-
-      mMaster->mAmpleAudioThreshold = std::max(
-        mMaster->mLowAudioThreshold * THRESHOLD_FACTOR,
-        mMaster->mAmpleAudioThreshold);
-
-      SLOG("Slow video decode, set "
-           "mLowAudioThreshold=%" PRId64
-           " mAmpleAudioThreshold=%" PRId64,
-           mMaster->mLowAudioThreshold.ToMicroseconds(),
-           mMaster->mAmpleAudioThreshold.ToMicroseconds());
-    }
-  }
-
   // At the start of decoding we want to "preroll" the decode until we've
   // got a few frames decoded before we consider whether decode is falling
   // behind. Otherwise our "we're falling behind" logic will trigger
@@ -2771,7 +2725,6 @@ MediaDecoderStateMachine::MediaDecoderStateMachine(MediaDecoder* aDecoder,
   INIT_WATCHABLE(mObservedDuration, TimeUnit()),
   mReader(new MediaDecoderReaderWrapper(mTaskQueue, aReader)),
   mPlaybackRate(1.0),
-  mLowAudioThreshold(detail::LOW_AUDIO_THRESHOLD),
   mAmpleAudioThreshold(detail::AMPLE_AUDIO_THRESHOLD),
   mAudioCaptured(false),
   mMinimizePreroll(aDecoder->GetMinimizePreroll()),

dom/media/MediaDecoderStateMachine.h

@@ -576,21 +576,8 @@ private:
   // Must hold monitor.
   uint32_t GetAmpleVideoFrames() const;
 
-  // Low audio threshold. If we've decoded less than this much audio we
-  // consider our audio decode "behind", and we may skip video decoding
-  // in order to allow our audio decoding to catch up. We favour audio
-  // decoding over video. We increase this threshold if we're slow to
-  // decode video frames, in order to reduce the chance of audio underruns.
-  // Note that we don't ever reset this threshold, it only ever grows as
-  // we detect that the decode can't keep up with rendering.
-  media::TimeUnit mLowAudioThreshold;
-
   // Our "ample" audio threshold. Once we've this much audio decoded, we
-  // pause decoding. If we increase mLowAudioThreshold, we'll also
-  // increase this too appropriately (we don't want mLowAudioThreshold
-  // to be greater than mAmpleAudioThreshold, else we'd stop decoding!).
-  // Note that we don't ever reset this threshold, it only ever grows as
-  // we detect that the decode can't keep up with rendering.
+  // pause decoding.
   media::TimeUnit mAmpleAudioThreshold;
 
   // Only one of a given pair of ({Audio,Video}DataPromise, WaitForDataPromise)