media/vpx: Add support for VP9 alpha channel

media/filters/vpx_video_decoder.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_FILTERS_VPX_VIDEO_DECODER_H_
 #define MEDIA_FILTERS_VPX_VIDEO_DECODER_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
@@ skipping 37 matching lines @@
 
  private:
   enum DecoderState {
     kUninitialized,
     kNormal,
     kFlushCodec,
     kDecodeFinished,
     kError
   };
 
+  // Return values for decoding alpha plane.
+  enum AlphaDecodeStatus {
+    kAlphaPlaneProcessed,  // Alpha plane (if found) was decoded successfully.
+    kNoAlphaPlaneData,  // Alpha plane was found, but decoder did not return any
+                        // data.
+    kAlphaPlaneError  // Fatal error occured when trying to decode alpha plane.
+  };
+
   // Handles (re-)initializing the decoder with a (new) config.
   // Returns true when initialization was successful.
   bool ConfigureDecoder(const VideoDecoderConfig& config);
 
   void CloseDecoder();
 
   // Helper method for decoding buffers either on the offload thread or directly
   // on the media thread. |bound_decode_cb| must be bound to the thread that
   // called Decode().
   void DecodeBuffer(const scoped_refptr<DecoderBuffer>& buffer,
                     const DecodeCB& bound_decode_cb);
 
   // Try to decode |buffer| into |video_frame|. Return true if all decoding
   // succeeded. Note that decoding can succeed and still |video_frame| be
   // nullptr if there has been a partial decoding.
   bool VpxDecode(const scoped_refptr<DecoderBuffer>& buffer,
                  scoped_refptr<VideoFrame>* video_frame);
 
   bool CopyVpxImageToVideoFrame(const struct vpx_image* vpx_image,
+                                const struct vpx_image* vpx_image_alpha,
                                 scoped_refptr<VideoFrame>* video_frame);
 
+  AlphaDecodeStatus DecodeAlphaPlane(
+      const struct vpx_image* vpx_image,
+      const struct vpx_image** vpx_image_alpha,
+      const scoped_refptr<DecoderBuffer>& buffer);
+
   base::ThreadChecker thread_checker_;
 
   // |state_| must only be read and written to on |offload_task_runner_| if it
   // is non-null and there are outstanding tasks on the offload thread.
   DecoderState state_;
 
   OutputCB output_cb_;
 
   VideoDecoderConfig config_;
 
@@ skipping 10 matching lines @@
   scoped_refptr<base::SingleThreadTaskRunner> offload_task_runner_;
 
   VideoFramePool frame_pool_;
 
   DISALLOW_COPY_AND_ASSIGN(VpxVideoDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_VPX_VIDEO_DECODER_H_