Improve audio/video sync during underflow, reduce underflow frequency.

media/renderers/video_renderer_impl.cc

Index: media/renderers/video_renderer_impl.cc
diff --git a/media/renderers/video_renderer_impl.cc b/media/renderers/video_renderer_impl.cc
index 2bb4547263f4ed6b6e4b4b9fff805590591f33a0..c89aa1d11ed279580cfbca1382a2f831df728c47 100644
--- a/media/renderers/video_renderer_impl.cc
+++ b/media/renderers/video_renderer_impl.cc
@@ -504,9 +504,45 @@ void VideoRendererImpl::FrameReady(VideoFrameStream::Status status,
       AddReadyFrame_Locked(frame);
     }
 
+    // Background rendering updates may not be ticking fast enough by itself to
+    // remove expired frames, so give it a boost here by ensuring we don't exit
+    // the decoding cycle too early.
+    //
+    // Similarly, if we've paused for underflow, remove all frames which are
+    // before the current media time.
+    const bool have_nothing = buffering_state_ != BUFFERING_HAVE_ENOUGH;
+    const bool have_nothing_and_paused = have_nothing && !sink_started_;
+    if (was_background_rendering_ ||
+        (use_new_video_renderering_path_ && have_nothing_and_paused &&
+         drop_frames_)) {
+      base::TimeTicks expiry_time;
+      if (have_nothing_and_paused) {
+        // Use the current media wall clock time plus the frame duration since
+        // RemoveExpiredFrames() is expecting the end point of an interval (it
+        // will subtract from the given value).
+        std::vector<base::TimeTicks> current_time;
+        wall_clock_time_cb_.Run(std::vector<base::TimeDelta>(), &current_time);
+        expiry_time = current_time[0] + algorithm_->average_frame_duration();
+      } else {
+        expiry_time = tick_clock_->NowTicks();
+      }
+
+      // Prior to rendering the first frame, |have_nothing_and_paused| will be
+      // true, correspondingly the |expiry_time| will be null; in this case
+      // there's no reason to try and remove any frames.
+      if (!expiry_time.is_null()) {
+        const size_t removed_frames =
+            algorithm_->RemoveExpiredFrames(expiry_time);
+
+        // Frames removed during underflow should be counted as dropped.
+        if (have_nothing_and_paused && removed_frames)
+          frames_dropped_ += removed_frames;
+      }
+    }
+
     // Signal buffering state if we've met our conditions for having enough
     // data.
-    if (buffering_state_ != BUFFERING_HAVE_ENOUGH && HaveEnoughData_Locked()) {
+    if (have_nothing && HaveEnoughData_Locked()) {
       TransitionToHaveEnough_Locked();
       if (use_new_video_renderering_path_ && !sink_started_ &&
           !rendered_end_of_stream_) {
@@ -516,14 +552,6 @@ void VideoRendererImpl::FrameReady(VideoFrameStream::Status status,
       }
     }
 
-    // Background rendering updates may not be ticking fast enough by itself to
-    // remove expired frames, so give it a boost here by ensuring we don't exit
-    // the decoding cycle too early.
-    if (was_background_rendering_) {
-      DCHECK(use_new_video_renderering_path_);
-      algorithm_->RemoveExpiredFrames(tick_clock_->NowTicks());
-    }
-
     // Always request more decoded video if we have capacity. This serves two
     // purposes:
     //   1) Prerolling while paused
@@ -711,6 +739,7 @@ void VideoRendererImpl::StartSink() {
 void VideoRendererImpl::StopSink() {
   DCHECK(task_runner_->BelongsToCurrentThread());
   sink_->Stop();
+  algorithm_->set_time_stopped();
   sink_started_ = false;
   was_background_rendering_ = false;
 }