media/filters/ffmpeg_glue.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.

// FFmpegGlue is an adapter for FFmpeg's URLProtocol interface that allows us to
// use a DataSource implementation with FFmpeg.  For convenience we use FFmpeg's
// avformat_open_input() function, which analyzes the filename given to it and
// automatically initializes the appropriate URLProtocol.
//
// Since the DataSource is already open by time we call avformat_open_input(),
// we need a way for avformat_open_input() to find the correct DataSource
// instance.  The solution is to maintain a map of "filenames" to DataSource
// instances, where filenames are actually just a unique identifier.  For
// simplicity, FFmpegGlue is registered as an HTTP handler and generates
// filenames based on the memory address of the DataSource, i.e.,
// http://0xc0bf4870.  Since there may be multiple FFmpegDemuxers active at one
// time, FFmpegGlue is a thread-safe singleton.
//
// Usage: FFmpegDemuxer adds the DataSource to FFmpegGlue's map and is given a
// filename to pass to avformat_open_input().  FFmpegDemuxer calls
// avformat_open_input() with the filename, which results in FFmpegGlue
// returning the DataSource as a URLProtocol instance to FFmpeg.  Since
// FFmpegGlue is only needed for opening files, when avformat_open_input()
// returns FFmpegDemuxer removes the DataSource from FFmpegGlue's map.

#ifndef MEDIA_FILTERS_FFMPEG_GLUE_H_
#define MEDIA_FILTERS_FFMPEG_GLUE_H_

#include <map>
#include <string>

#include "base/memory/singleton.h"
#include "base/synchronization/lock.h"
#include "media/base/media_export.h"

struct URLProtocol;

namespace media {

class MEDIA_EXPORT FFmpegURLProtocol {
 public:
  FFmpegURLProtocol() {}

  virtual ~FFmpegURLProtocol() {}

  // Read the given amount of bytes into data, returns the number of bytes read
  // if successful, kReadError otherwise.
  virtual size_t Read(size_t size, uint8* data) = 0;

  // Returns true and the current file position for this file, false if the
  // file position could not be retrieved.
  virtual bool GetPosition(int64* position_out) = 0;

  // Returns true if the file position could be set, false otherwise.
  virtual bool SetPosition(int64 position) = 0;

  // Returns true and the file size, false if the file size could not be
  // retrieved.
  virtual bool GetSize(int64* size_out) = 0;

  // Returns false if this protocol supports random seeking.
  virtual bool IsStreaming() = 0;

 private:
  DISALLOW_COPY_AND_ASSIGN(FFmpegURLProtocol);
};

class MEDIA_EXPORT FFmpegGlue {
 public:
  // Returns the singleton instance.
  static FFmpegGlue* GetInstance();

  // Adds a FFmpegProtocol to the FFmpeg glue layer and returns a unique string
  // that can be passed to FFmpeg to identify the data source.
  std::string AddProtocol(FFmpegURLProtocol* protocol);

  // Removes a FFmpegProtocol from the FFmpeg glue layer.  Using strings from
  // previously added FFmpegProtocols will no longer work.
  void RemoveProtocol(FFmpegURLProtocol* protocol);

  // Assigns the FFmpegProtocol identified with by the given key to
  // |protocol|, or assigns NULL if no such FFmpegProtocol could be found.
  void GetProtocol(const std::string& key,
                   FFmpegURLProtocol** protocol);

 private:
  // Only allow Singleton to create and delete FFmpegGlue.
  friend struct DefaultSingletonTraits<FFmpegGlue>;
  FFmpegGlue();
  virtual ~FFmpegGlue();

  // Returns the unique key for this data source, which can be passed to
  // avformat_open_input() as the filename.
  std::string GetProtocolKey(FFmpegURLProtocol* protocol);

  // Mutual exclusion while adding/removing items from the map.
  base::Lock lock_;

  // Map between keys and FFmpegProtocol references.
  typedef std::map<std::string, FFmpegURLProtocol*> ProtocolMap;
  ProtocolMap protocols_;

  friend class FFmpegGlueTest;
  static URLProtocol* url_protocol();

  DISALLOW_COPY_AND_ASSIGN(FFmpegGlue);
};

}  // namespace media

#endif  // MEDIA_FILTERS_FFMPEG_GLUE_H_