Allow media track switching.

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 918c37b111723422929159898c10f3dbcf553d93..437d55c45ddf82b9aaa43e958e492c8b54fa2651 100644
--- a/media/renderers/video_renderer_impl.cc
+++ b/media/renderers/video_renderer_impl.cc
@@ -31,7 +31,7 @@ VideoRendererImpl::VideoRendererImpl(
     const scoped_refptr<base::SingleThreadTaskRunner>& media_task_runner,
     const scoped_refptr<base::TaskRunner>& worker_task_runner,
     VideoRendererSink* sink,
-    ScopedVector<VideoDecoder> decoders,
+    const CreateVideoDecodersCB& create_video_decoders_cb,
     bool drop_frames,
     GpuVideoAcceleratorFactories* gpu_factories,
     const scoped_refptr<MediaLog>& media_log)
@@ -39,15 +39,16 @@ VideoRendererImpl::VideoRendererImpl(
       sink_(sink),
       sink_started_(false),
       client_(nullptr),
-      video_frame_stream_(new VideoFrameStream(media_task_runner,
-                                               std::move(decoders),
-                                               media_log)),
+      video_frame_stream_(nullptr),

[xhwang, 2017/03/27 19:13:53]

not needed

[servolk, 2017/03/27 22:34:13]

Done.

       gpu_memory_buffer_pool_(nullptr),
       media_log_(media_log),
       low_delay_(false),
       received_end_of_stream_(false),
       rendered_end_of_stream_(false),
       state_(kUninitialized),
+      create_video_decoders_cb_(create_video_decoders_cb),
+      gpu_factories_(gpu_factories),
+      worker_task_runner_(worker_task_runner),
       pending_read_(false),
       drop_frames_(drop_frames),
       buffering_state_(BUFFERING_HAVE_NOTHING),
@@ -63,11 +64,7 @@ VideoRendererImpl::VideoRendererImpl(
       max_buffered_frames_(limits::kMaxVideoFrames),
       weak_factory_(this),
       frame_callback_weak_factory_(this) {
-  if (gpu_factories &&
-      gpu_factories->ShouldUseGpuMemoryBuffersForVideoFrames()) {
-    gpu_memory_buffer_pool_.reset(new GpuMemoryBufferVideoFramePool(
-        media_task_runner, worker_task_runner, gpu_factories));
-  }
+  DCHECK(!create_video_decoders_cb_.is_null());
 }
 
 VideoRendererImpl::~VideoRendererImpl() {
@@ -150,10 +147,18 @@ void VideoRendererImpl::Initialize(
   DCHECK_EQ(stream->type(), DemuxerStream::VIDEO);
   DCHECK(!init_cb.is_null());
   DCHECK(!wall_clock_time_cb.is_null());
-  DCHECK_EQ(kUninitialized, state_);
+  DCHECK(kUninitialized == state_ || kFlushed == state_);
   DCHECK(!was_background_rendering_);
   DCHECK(!time_progressing_);
-  DCHECK(!have_renderered_frames_);
+
+  ScopedVector<VideoDecoder> decoders = create_video_decoders_cb_.Run();
+  video_frame_stream_.reset(
+      new VideoFrameStream(task_runner_, std::move(decoders), media_log_));
+  if (gpu_factories_ &&
+      gpu_factories_->ShouldUseGpuMemoryBuffersForVideoFrames()) {
+    gpu_memory_buffer_pool_.reset(new GpuMemoryBufferVideoFramePool(
+        task_runner_, worker_task_runner_, gpu_factories_));

[xhwang, 2017/03/27 19:13:53]

OOC, why do we need to create a new GpuMemoryBufferVideoFramePool upon reinit?
If there's a legit reason, add a comment?

[servolk, 2017/03/27 22:34:13]

Well, if we are switching from let's say 8-bit H264 video track to a 10bit H264
track, then the GPU buffers would probably need to be reallocated. I've added a
comment about it.
Also, I think we can save a some memory by adding an else clause an releasing
|gpu_memory_buffer_pool_| if we know GPU is not going to be used.

+  }
 
   low_delay_ = (stream->liveness() == DemuxerStream::LIVENESS_LIVE);
   UMA_HISTOGRAM_BOOLEAN("Media.VideoRenderer.LowDelay", low_delay_);