[cast] Add optional VideoEncoder method to flush frames.

media/cast/cast_config.h

 // Copyright 2013 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_CAST_CAST_CONFIG_H_
 #define MEDIA_CAST_CAST_CONFIG_H_
 
 #include <list>
 #include <string>
 #include <vector>
@@ skipping 79 matching lines @@
   int width;  // Incoming frames will be scaled to this size.
   int height;
 
   float congestion_control_back_off;
   int max_bitrate;
   int min_bitrate;
   int start_bitrate;
   int max_qp;
   int min_qp;
   int max_frame_rate;  // TODO(miu): Should be double, not int.
-  int max_number_of_video_buffers_used;  // Max value depend on codec.
+
+  // This field is used differently by various encoders. It defaults to 1.
+  //
+  // For VP8, it should be 1 to operate in single-buffer mode, or 3 to operate
+  // in multi-buffer mode. See
+  // http://www.webmproject.org/docs/encoder-parameters/ for details.
+  //
+  // For H.264 on Mac or iOS, it controls the max number of frames the encoder
+  // may hold before emitting a frame. A larger window may allow higher encoding
+  // efficiency at the cost of latency and memory. Set to 0 to let the encoder
+  // choose a suitable value for the platform and other encoding settings.
+  int max_number_of_video_buffers_used;
+
   Codec codec;
   int number_of_encode_threads;
 
   // The AES crypto key and initialization vector.  Each of these strings
   // contains the data in binary form, of size kAesKeySize.  If they are empty
   // strings, crypto is not being used.
   std::string aes_key;
   std::string aes_iv_mask;
 };
 
@@ skipping 65 matching lines @@
 typedef base::Callback<void(scoped_ptr<base::SharedMemory>)>
     ReceiveVideoEncodeMemoryCallback;
 typedef base::Callback<void(size_t size,
                             const ReceiveVideoEncodeMemoryCallback&)>
     CreateVideoEncodeMemoryCallback;
 
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_CAST_CONFIG_H_