rendering_helper - Drop frames if the decoder cannot catch up.

content/common/gpu/media/rendering_helper.cc

Index: content/common/gpu/media/rendering_helper.cc
diff --git a/content/common/gpu/media/rendering_helper.cc b/content/common/gpu/media/rendering_helper.cc
index 00e85f9f0ecd0c44b1961175d1fc5ce248670712..d6621c92a56ae663e37736aa980587715562e953 100644
--- a/content/common/gpu/media/rendering_helper.cc
+++ b/content/common/gpu/media/rendering_helper.cc
@@ -75,7 +75,7 @@ VideoFrameTexture::~VideoFrameTexture() {
 }
 
 RenderingHelper::RenderedVideo::RenderedVideo()
-    : last_frame_rendered(false), is_flushing(false) {
+    : last_frame_rendered(false), is_flushing(false), frames_to_drop(0) {
 }
 
 RenderingHelper::RenderedVideo::~RenderedVideo() {
@@ -398,6 +398,11 @@ void RenderingHelper::QueueVideoFrame(
   RenderedVideo* video = &videos_[window_id];
   DCHECK(!video->is_flushing);
 
+  if (video->frames_to_drop > 0) {
+    --video->frames_to_drop;

[acolwell GONE FROM CHROMIUM, 2014/09/16 19:10:39]

Is this frame dropping visible outside this code in some way? Web applications
need to be able to observe this via HTMLVideoElement::webkitDroppedFrameCount()
and VideoPlaybackQuality::droppedVideoFrame() so that they can adapt the content
downward to avoid overtaxing the decoder.

[Owen Lin, 2014/09/17 02:48:35]

The code is only used in the vda_unittest. It won't affect others.

+    return;
+  }
+
   // Pop the last frame if it has been rendered.
   if (video->last_frame_rendered) {
     // When last_frame_rendered is true, we should have only one pending frame.
@@ -525,6 +530,9 @@ void RenderingHelper::RenderContent() {
       GLSetViewPort(video->render_area);
       RenderTexture(frame->texture_target(), frame->texture_id());
 
+      if (video->last_frame_rendered)

[Pawel Osciak, 2014/09/15 14:09:34]

Please note here that we won't start dropping before first frame is queued via
QueueVideoFrame, because initially last_frame_rendered is false, which means
that we don't drop if the first frame is delivered late.
And the above behavior is ok from the point of view of the test framework that
counts frames, it will still catch late first decode, right?

[Owen Lin, 2014/09/16 01:38:34]

That's the expected behavior, we always wait for the first frame.
We have a metrics on the delivery time of the first frame in the VDAPerf test so
we still catch this kind of bugs.

+        ++video->frames_to_drop;
+
       if (video->pending_frames.size() > 1 || video->is_flushing) {
         frames_to_be_returned.push_back(video->pending_frames.front());
         video->pending_frames.pop();