media/base/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_BASE_VIDEO_DECODER_H_
#define MEDIA_BASE_VIDEO_DECODER_H_

#include "base/callback.h"
#include "base/memory/ref_counted.h"
#include "media/base/pipeline_status.h"
#include "media/base/media_export.h"
#include "ui/gfx/size.h"

namespace media {

class DemuxerStream;
class VideoFrame;

class MEDIA_EXPORT VideoDecoder
    : public base::RefCountedThreadSafe<VideoDecoder> {
 public:
  // Status codes for read operations on VideoDecoder.
  enum Status {
    kOk,  // Everything went as planned.
    kDecodeError,  // Decoding error happened.
    kDecryptError  // Decrypting error happened.
  };

  // Initialize a VideoDecoder with the given DemuxerStream, executing the
  // callback upon completion.
  // statistics_cb is used to update global pipeline statistics.
  virtual void Initialize(const scoped_refptr<DemuxerStream>& stream,
                          const PipelineStatusCB& status_cb,
                          const StatisticsCB& statistics_cb) = 0;

  // Requests a frame to be decoded. The status of the decoder and decoded frame
  // are returned via the provided callback. Only one read may be in flight at
  // any given time.
  //
  // Implementations guarantee that the callback will not be called from within
  // this method.
  //
  // If the returned status is not kOk, some error has occurred in the video
  // decoder. In this case, the returned frame should always be NULL.
  //
  // Otherwise, the video decoder is in good shape. In this case, Non-NULL
  // frames contain decoded video data or may indicate the end of the stream.
  // NULL video frames indicate an aborted read. This can happen if the
  // DemuxerStream gets flushed and doesn't have any more data to return.
  typedef base::Callback<void(Status, const scoped_refptr<VideoFrame>&)> ReadCB;
  virtual void Read(const ReadCB& read_cb) = 0;

  // Reset decoder state, fulfilling all pending ReadCB and dropping extra
  // queued decoded data. After this call, the decoder is back to an initialized
  // clean state.
  virtual void Reset(const base::Closure& closure) = 0;

  // Stop decoder and set it to an uninitialized state. Note that a VideoDecoder
  // should/could not be re-initialized after it has been stopped.
  virtual void Stop(const base::Closure& closure) = 0;

  // Returns true if the output format has an alpha channel. Most formats do not
  // have alpha so the default is false. Override and return true for decoders
  // that return formats with an alpha channel.
  virtual bool HasAlpha() const;

  // Prepare decoder for shutdown.  This is a HACK needed because
  // PipelineImpl::Stop() goes through a Pause/Flush/Stop dance to all its
  // filters, waiting for each state transition to complete before starting the
  // next, but WebMediaPlayerImpl::Destroy() holds the renderer loop hostage for
  // the duration.  Default implementation does nothing; derived decoders may
  // override as needed.  http://crbug.com/110228 tracks removing this.
  virtual void PrepareForShutdownHack();

 protected:
  friend class base::RefCountedThreadSafe<VideoDecoder>;
  virtual ~VideoDecoder();
  VideoDecoder();

  DISALLOW_COPY_AND_ASSIGN(VideoDecoder);
};

}  // namespace media

#endif  // MEDIA_BASE_VIDEO_DECODER_H_