Checking in media::FFmpegGlue and some common FFmpeg code.

media/filters/ffmpeg_glue.h

Index: media/filters/ffmpeg_glue.h
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+// Copyright (c) 2009 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
+// av_open_input_file function, which analyzes the filename given to it and
+// automatically initializes the appropriate URLProtocol.
+//
+// Since the DataSource is already open by time we call av_open_input_file, we
+// need a way for av_open_input_file 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 av_open_input_file.  FFmpegDemuxer calls
+// av_open_input_file 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 av_open_input_file 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/lock.h"
+#include "base/singleton.h"
+
+// FFmpeg forward declarations.
+struct URLContext;
+typedef int64 offset_t;
+
+namespace media {
+
+class DataSource;
+
+class FFmpegGlue : public Singleton<FFmpegGlue> {
+ public:
+  // Adds a DataSource to the FFmpeg glue layer and returns a unique string that
+  // can be passed to FFmpeg to identify the data source.
+  std::string AddDataSource(DataSource* data_source);
+
+  // Removes a DataSource from the FFmpeg glue layer.  Using strings from
+  // previously added DataSources will no longer work.
+  void RemoveDataSource(DataSource* data_source);
+
+  // Assigns the DataSource identified with by the given key to |data_source|,
+  // or assigns NULL if no such DataSource could be found.
+  void GetDataSource(const std::string& key,
+                     scoped_refptr<DataSource>* data_source);
+
+ 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
+  // av_open_input_file as the filename.
+  std::string GetDataSourceKey(DataSource* data_source);
+
+  // Mutual exclusion while adding/removing items from the map.
+  Lock lock_;
+
+  // Map between keys and DataSource references.
+  typedef std::map< std::string, scoped_refptr<DataSource> > DataSourceMap;
+  DataSourceMap data_sources_;
+
+  DISALLOW_COPY_AND_ASSIGN(FFmpegGlue);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_FFMPEG_GLUE_H_