Cast: Improve AV sync slightly

This is an interim solution before we can pass TimeTicks associated with
a video frame to the cast library. We use base::TimeTicks::Now() when
a frame is delivered to the render process as the timestamp of the
frame. This improves AV sync slightly according to the performance test.

Before

*RESULT CastV2Performance_gpu_24fps: av_sync= {15.520811,10.694887} ms
*RESULT CastV2Performance_gpu_30fps: av_sync= {7.877492,14.865763} ms
*RESULT CastV2Performance_gpu_60fps: av_sync= {-15.974133,10.762621} ms

After

*RESULT CastV2Performance_gpu_24fps: av_sync= {9.231218,10.886808} ms
*RESULT CastV2Performance_gpu_30fps: av_sync= {10.161435,10.176140} ms
*RESULT CastV2Performance_gpu_60fps: av_sync= {-10.761692,12.102184} ms

R=hubbe@chromium.org

Review URL: https://codereview.chromium.org/273753003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269112 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 3 insertions, 13 deletions

diff --git a/chrome/renderer/media/cast_rtp_stream.cc b/chrome/renderer/media/cast_rtp_stream.cc
index 99a8543..5557582 100644
--- a/chrome/renderer/media/cast_rtp_stream.cc
+++ b/chrome/renderer/media/cast_rtp_stream.cc
@@ -230,24 +230,15 @@ class CastVideoSink : public base::SupportsWeakPtr<CastVideoSink>,
       return;
     }
 
-    // Capture time is calculated using the time when the first frame
-    // is delivered. Doing so has less jitter because each frame has
-    // a TimeDelta from the first frame. However there is a delay between
-    // capture and delivery here for the first frame. We do not account
-    // for this delay.
-    if (first_frame_timestamp_.is_null())
-      first_frame_timestamp_ = base::TimeTicks::Now() - frame->timestamp();
+    const base::TimeTicks now = base::TimeTicks::Now();
 
     // Used by chrome/browser/extension/api/cast_streaming/performance_test.cc
     TRACE_EVENT_INSTANT2(
         "mirroring", "MediaStreamVideoSink::OnVideoFrame",
         TRACE_EVENT_SCOPE_THREAD,
-        "timestamp",
-        (first_frame_timestamp_ + frame->timestamp()).ToInternalValue(),
+        "timestamp",  now.ToInternalValue(),
         "time_delta", frame->timestamp().ToInternalValue());
-
-    frame_input_->InsertRawVideoFrame(
-        frame, first_frame_timestamp_ + frame->timestamp());
+    frame_input_->InsertRawVideoFrame(frame, now);
   }
 
   // Attach this sink to a video track represented by |track_|.
@@ -267,7 +258,6 @@ class CastVideoSink : public base::SupportsWeakPtr<CastVideoSink>,
   bool sink_added_;
   gfx::Size expected_coded_size_;
   CastRtpStream::ErrorCallback error_callback_;
-  base::TimeTicks first_frame_timestamp_;
 
   DISALLOW_COPY_AND_ASSIGN(CastVideoSink);
 };