Bug 1219134: P2. Use LibAV/FFmpeg logic to detect invalid pts. r=edwin

The logic was extracted from LibAV cmdutils.c. FFmpeg provides an API for that (av_frame_get_best_effort_timestamp()) unfortunately this isn't provided by LibAV.
So copy the logic instead in order to keep compatibility with the two forks.

dom/media/platforms/ffmpeg/FFmpegDataDecoder.cpp

@@ -21,6 +21,45 @@ namespace mozilla
 bool FFmpegDataDecoder<LIBAV_VER>::sFFmpegInitDone = false;
 StaticMutex FFmpegDataDecoder<LIBAV_VER>::sMonitor;
 
+FFmpegDataDecoder<LIBAV_VER>::PtsCorrectionContext::PtsCorrectionContext()
+  : mNumFaultyPts(0)
+  , mNumFaultyDts(0)
+  , mLastPts(INT64_MIN)
+  , mLastDts(INT64_MIN)
+{
+}
+
+int64_t
+FFmpegDataDecoder<LIBAV_VER>::PtsCorrectionContext::GuessCorrectPts(int64_t aPts, int64_t aDts)
+{
+  int64_t pts = AV_NOPTS_VALUE;
+
+  if (aDts != int64_t(AV_NOPTS_VALUE)) {
+    mNumFaultyDts += aDts <= mLastDts;
+    mLastDts = aDts;
+  }
+  if (aPts != int64_t(AV_NOPTS_VALUE)) {
+    mNumFaultyPts += aPts <= mLastPts;
+    mLastPts = aPts;
+  }
+  if ((mNumFaultyPts <= mNumFaultyDts || aDts == int64_t(AV_NOPTS_VALUE)) &&
+      aPts != int64_t(AV_NOPTS_VALUE)) {
+    pts = aPts;
+  } else {
+    pts = aDts;
+  }
+  return pts;
+}
+
+void
+FFmpegDataDecoder<LIBAV_VER>::PtsCorrectionContext::Reset()
+{
+  mNumFaultyPts = 0;
+  mNumFaultyDts = 0;
+  mLastPts = INT64_MIN;
+  mLastDts = INT64_MIN;
+}
+
 FFmpegDataDecoder<LIBAV_VER>::FFmpegDataDecoder(FlushableTaskQueue* aTaskQueue,
                                                 MediaDataDecoderCallback* aCallback,
                                                 AVCodecID aCodecID)
@@ -184,6 +223,7 @@ FFmpegDataDecoder<LIBAV_VER>::ProcessFlush()
   if (mCodecContext) {
     avcodec_flush_buffers(mCodecContext);
   }
+  mPtsContext.Reset();
   MonitorAutoLock mon(mMonitor);
   mIsFlushing = false;
   mon.NotifyAll();

dom/media/platforms/ffmpeg/FFmpegDataDecoder.h

@@ -63,6 +63,21 @@ protected:
   Atomic<bool> mIsFlushing;
   AVCodecParserContext* mCodecParser;
 
+  class PtsCorrectionContext {
+  public:
+    PtsCorrectionContext();
+    int64_t GuessCorrectPts(int64_t aPts, int64_t aDts);
+    void Reset();
+
+  private:
+    int64_t mNumFaultyPts; /// Number of incorrect PTS values so far
+    int64_t mNumFaultyDts; /// Number of incorrect DTS values so far
+    int64_t mLastPts;       /// PTS of the last frame
+    int64_t mLastDts;       /// DTS of the last frame
+  };
+
+  PtsCorrectionContext mPtsContext;
+
 private:
   static bool sFFmpegInitDone;
   static StaticMutex sMonitor;

dom/media/platforms/ffmpeg/FFmpegH264Decoder.cpp

@@ -54,21 +54,6 @@ FFmpegH264Decoder<LIBAV_VER>::Init()
   return InitPromise::CreateAndResolve(TrackInfo::kVideoTrack, __func__);
 }
 
-int64_t
-FFmpegH264Decoder<LIBAV_VER>::GetPts(const AVPacket& packet)
-{
-  MOZ_ASSERT(mTaskQueue->IsCurrentThreadIn());
-#if LIBAVCODEC_VERSION_MAJOR == 53
-  if (mFrame->pkt_pts == 0) {
-    return mFrame->pkt_dts;
-  } else {
-    return mFrame->pkt_pts;
-  }
-#else
-  return mFrame->pkt_pts;
-#endif
-}
-
 FFmpegH264Decoder<LIBAV_VER>::DecodeResult
 FFmpegH264Decoder<LIBAV_VER>::DoDecodeFrame(MediaRawData* aSample)
 {
@@ -158,7 +143,7 @@ FFmpegH264Decoder<LIBAV_VER>::DoDecodeFrame(MediaRawData* aSample,
 
   // If we've decoded a frame then we need to output it
   if (decoded) {
-    int64_t pts = GetPts(packet);
+    int64_t pts = mPtsContext.GuessCorrectPts(mFrame->pkt_pts, mFrame->pkt_dts);
     FFMPEG_LOG("Got one frame output with pts=%lld opaque=%lld",
                pts, mCodecContext->reordered_opaque);
 

dom/media/platforms/ffmpeg/FFmpegH264Decoder.h

@@ -59,7 +59,6 @@ private:
 
   static int AllocateBufferCb(AVCodecContext* aCodecContext, AVFrame* aFrame);
   static void ReleaseBufferCb(AVCodecContext* aCodecContext, AVFrame* aFrame);
-  int64_t GetPts(const AVPacket& packet);
 
   RefPtr<ImageContainer> mImageContainer;
   uint32_t mPictureWidth;