Add SupportsConfigChanges() to DemuxerStream.

media/base/demuxer_stream.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_DEMUXER_STREAM_H_
 #define MEDIA_BASE_DEMUXER_STREAM_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "media/base/media_export.h"
@@ skipping 22 matching lines @@
   //             return. The second parameter MUST be NULL when this status is
   //             returned.
   //  kConfigChange : Indicates that the AudioDecoderConfig or
   //                  VideoDecoderConfig for the stream has changed.
   //                  The DemuxerStream expects an audio_decoder_config() or
   //                  video_decoder_config() call before Read() will start
   //                  returning DecoderBuffers again. The decoder will need this
   //                  new configuration to properly decode the buffers read
   //                  from this point forward. The second parameter MUST be NULL
   //                  when this status is returned.
+  //                  This will only be returned if SupportsConfigChanges()
+  //                  returns 'true' for this DemuxerStream.
   enum Status {
     kOk,
     kAborted,
     kConfigChanged,
   };
 
   // Request a buffer to returned via the provided callback.
   //
   // The first parameter indicates the status of the read.
   // The second parameter is non-NULL and contains media data
   // or the end of the stream if the first parameter is kOk. NULL otherwise.
   typedef base::Callback<void(Status,
                               const scoped_refptr<DecoderBuffer>&)>ReadCB;
   virtual void Read(const ReadCB& read_cb) = 0;
 
   // Returns the audio decoder configuration. It is an error to call this method
   // if type() != AUDIO.
   virtual AudioDecoderConfig audio_decoder_config() = 0;
 
   // Returns the video decoder configuration. It is an error to call this method
   // if type() != VIDEO.
   virtual VideoDecoderConfig video_decoder_config() = 0;
 
   // Returns the type of stream.
   virtual Type type() = 0;
 
   virtual void EnableBitstreamConverter() = 0;
 
+  // Whether or not this DemuxerStream allows midstream configuration changes.
+  //
+  // A DemuxerStream that returns 'true' to this may return the 'kConfigChange'
+  // status from a Read() call. In this case the client is expected to be
+  // capable of taking appropriate action to handle config changes. Otherwise
+  // audio_decoder_config() and video_decoder_config()'s return values are
+  // guaranteed to remain constant, and the client may make optimizations based
+  // on this.
+  virtual bool SupportsConfigChanges() = 0;
+
  protected:
   // Only allow concrete implementations to get deleted.
   virtual ~DemuxerStream();
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DEMUXER_STREAM_H_