Switch to AVIO instead of a custom FFmpeg URLProtocol handler.

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.
+// FFmpegGlue is an interface between FFmpeg and Chrome used to proxy FFmpeg's
+// read and seek requests to Chrome's internal data structures.  The glue works
+// through the AVIO interface provided by FFmpeg.
 //
-// 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.
+// AVIO works through a special AVIOContext created through avio_alloc_context()
+// which is attached to the AVFormatContext used for demuxing.  The AVIO context
+// is initialized with read and seek methods which FFmpeg calls when necessary.
 //
-// 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.
+// During OpenContext() FFmpegGlue will tell FFmpeg to use Chrome's AVIO context
+// by passing NULL in for the filename parameter to avformat_open_input().  All
+// FFmpeg operations using the configured AVFormatContext will then redirect
+// reads and seeks through the glue.
+//
+// The glue in turn processes those read and seek requests using the
+// FFmpegURLProtocol provided during construction.
+//
+// FFmpegGlue is also responsible for initializing FFmpeg, which is done once
+// per process.  Initialization includes: turning off log messages, registering
+// a lock manager, and finally registering all demuxers and codecs.
 
 #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 "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
 #include "media/base/media_export.h"
 
-struct URLProtocol;
+struct AVFormatContext;
+struct AVIOContext;
 
 namespace media {
 
+class ScopedPtrAVFree;
+
 class MEDIA_EXPORT FFmpegURLProtocol {
  public:
-  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;
+  virtual int Read(int 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;
-
- protected:
-  virtual ~FFmpegURLProtocol() {}
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(FFmpegURLProtocol);
 };
 
 class MEDIA_EXPORT FFmpegGlue {
  public:
-  // Returns the singleton instance.
-  static FFmpegGlue* GetInstance();
+  static void InitializeFFmpeg();
 
-  // 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);
+  explicit FFmpegGlue(FFmpegURLProtocol* protocol);

[scherkus (not reviewing), 2012/10/02 01:36:35]

seems like you may want to mention that the lifetime of |protocol| must exceed
the lifetime of FFmpegGlue

[DaleCurtis, 2012/10/02 01:46:30]

Whoops, documented everywhere in the unit tests, but not here :)

+  ~FFmpegGlue();
 
-  // 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);
+  // Opens an AVFormatContext specially prepared to process reads and seeks
+  // through the FFmpegURLProtocol provided during construction.
+  bool OpenContext();
+  AVFormatContext* format_context() { return format_context_; }
 
  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();
+  bool open_called_;
+  AVFormatContext* format_context_;
+  scoped_ptr_malloc<AVIOContext, ScopedPtrAVFree> avio_context_;
 
   DISALLOW_COPY_AND_ASSIGN(FFmpegGlue);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_FFMPEG_GLUE_H_