Allow multiple concurrent Decode() requests in VideoDecoder interface.

media/base/video_decoder.h

Index: media/base/video_decoder.h
diff --git a/media/base/video_decoder.h b/media/base/video_decoder.h
index 81b93f7778ba8dd0869aeb9bd777849dc17a3ddc..3e89fdf787a475c87013a39859d28f3bd51fc4b9 100644
--- a/media/base/video_decoder.h
+++ b/media/base/video_decoder.h
@@ -46,8 +46,10 @@ class MEDIA_EXPORT VideoDecoder {
                           const PipelineStatusCB& status_cb) = 0;
 
   // Requests a |buffer| to be decoded. The status of the decoder and decoded
-  // frame are returned via the provided callback. Only one decode may be in
-  // flight at any given time.
+  // frame are returned via the provided callback. Some decoders may allow
+  // decoding multiple frames in parallel. Callers should call
+  // GetMaxDecodeRequests() to get number of frames that may be decoded in

[xhwang, 2014/04/25 00:36:03]

s/frames/buffers

[Sergey Ulanov, 2014/04/26 00:59:29]

Done.

+  // parallel.
   //
   // Implementations guarantee that the callback will not be called from within
   // this method.
@@ -64,6 +66,8 @@ class MEDIA_EXPORT VideoDecoder {
   // Some VideoDecoders may queue up multiple VideoFrames from a single
   // DecoderBuffer, if we have any such queued frames this will return the next
   // one. Otherwise we return a NULL VideoFrame.
+  //
+  // TODO(xhwang): Remove this method.

[xhwang, 2014/04/25 00:36:03]

s/Remove/Revisit

Since we still have 1:1 mapping b/w DecodeCB and input buffer, we'll still need
this for audio.

[Sergey Ulanov, 2014/04/26 00:59:29]

Done. I think the right way to fix it is to pass multiple output buffers in
DecodeCB - so this function won't be needed.

   virtual scoped_refptr<VideoFrame> GetDecodeOutput();
 
   // Resets decoder state, fulfilling all pending DecodeCB and dropping extra
@@ -88,6 +92,9 @@ class MEDIA_EXPORT VideoDecoder {
   // use a fixed set of VideoFrames for decoding.
   virtual bool CanReadWithoutStalling() const;
 
+  // Returns how many frames that may be decoded in parallel.

[xhwang, 2014/04/25 00:36:03]

s/frame/buffer

[Sergey Ulanov, 2014/04/26 00:59:29]

Done.

+  virtual int GetMaxDecodeRequests() const;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(VideoDecoder);
 };