Add accelerated video decoder interface, VP8 and H.264 implementations and hook up to V4L2SVDA.

content/common/gpu/media/accelerated_video_decoder.h

+// Copyright 2015 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 CONTENT_COMMON_GPU_MEDIA_ACCELERATED_VIDEO_DECODER_
+#define CONTENT_COMMON_GPU_MEDIA_ACCELERATED_VIDEO_DECODER_
+
+#include "base/callback_forward.h"
+#include "base/callback_helpers.h"
+#include "base/memory/ref_counted.h"

[Owen Lin, 2015/01/08 15:42:06]

not used for the above includes?

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

+#include "content/common/content_export.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace content {
+
+// An AcceleratedVideoDecoder is a video decoder that requires support from an
+// external accelerator (typically a hardware accelerator) to partially offload
+// the decode process after parsing stream headers, and performing reference
+// frame and state management.
+class CONTENT_EXPORT AcceleratedVideoDecoder {
+ public:
+  AcceleratedVideoDecoder() {}
+  virtual ~AcceleratedVideoDecoder() {}
+
+  virtual void SetStream(const uint8* ptr, size_t size) = 0;
+
+  // Have the decoder flush its state and trigger output of all previously
+  // decoded surfaces. Return false on failure.
+  virtual bool Flush() WARN_UNUSED_RESULT = 0;
+
+  // To be called during decoding.
+  // Stop (pause) decoding, discarding all remaining inputs and outputs,

[kcwu, 2015/01/09 10:07:47]

Make this first line.

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

+  // but do not flush decoder state, so that the playback can be resumed later,
+  // possibly from a different location.
+  virtual void Reset() = 0;
+
+  // Decode result codes.
+  enum DecResult {

[Owen Lin, 2015/01/08 15:42:06]

Use a full name, e.g., DecodeResult ?

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

+    kDecodeError,  // Error while decoding.
+    // TODO posciak: unsupported streams are currently treated as error

[kcwu, 2015/01/09 10:07:47]

TODO(posciak):

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

+    // in decoding; in future it could perhaps be possible to fall back
+    // to software decoding instead.
+    // kStreamError,  // Error in stream.
+    kAllocateNewSurfaces,  // Need a new set of surfaces to be allocated.
+    kRanOutOfStreamData,   // Need more stream data to proceed.
+    kRanOutOfSurfaces,     // Waiting for the client to free up output surfaces.
+  };
+
+  // Try to decode more of the stream, returning decoded frames asynchronously.
+  // Return when more stream is needed, when we run out of free surfaces, when
+  // we need a new set of them, or when an error occurs.
+  virtual DecResult Decode() WARN_UNUSED_RESULT = 0;

[Owen Lin, 2015/01/08 15:42:06]

How is the decoded frames be returned?

[Owen Lin, 2015/01/08 15:42:06]

Is this a blocking call? 
How many frame will be decoded? If not one, what happens if user want to seek or
stop the video?

[Pawel Osciak, 2015/01/09 13:50:31]

As many as there are in the buffer. The frames will be returned to client for
output via a callback before this returns, but the client may decide to drop
them if there is a seek. For stop, it will have to be after this bitstream
buffer.

But actually, we will always in practice get one frame per buffer in Chrome

[Pawel Osciak, 2015/01/09 13:50:31]

Via a separate callback. I don't have a generalized callback here in this
interface, because some decoders call Output(H264Picture) and some
Output(VP8Picture) and I haven't unified these classes enough. Perhaps in a
further redesign...

+
+  // Return dimensions/required number of output surfaces that client should
+  // be ready to provide for the decoder to function properly.
+  // To be used after Decode() returns kNeedNewSurfaces.
+  virtual gfx::Size GetPicSize() = 0;

[Owen Lin, 2015/01/08 15:42:06]

return "const gfx::Size&" ?

[kcwu, 2015/01/09 10:07:47]

GetPicSize() const = 0;

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

[Pawel Osciak, 2015/01/12 07:18:19]

Done.

+  virtual size_t GetRequiredNumOfPictures() = 0;

[kcwu, 2015/01/09 10:07:47]

...() const = 0;

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(AcceleratedVideoDecoder);

[Owen Lin, 2015/01/08 15:42:06]

You have put this under private: to make it works.

[Pawel Osciak, 2015/01/12 07:18:18]

Done.

+};
+
+}  //  namespace content
+
+#endif  // CONTENT_COMMON_GPU_MEDIA_ACCELERATED_VIDEO_DECODER_