Significantly increased max_num_buffers_ of Vp9FrameBufferPool.

webrtc/modules/video_coding/codecs/vp9/vp9_frame_buffer_pool.h

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  *
  */
@@ skipping 89 matching lines @@
   //             a pointer to one of the pool's Vp9FrameBuffer.
   static int32_t VpxReleaseFrameBuffer(void* user_priv,
                                        vpx_codec_frame_buffer* fb);
 
  private:
   // Protects |allocated_buffers_|.
   rtc::CriticalSection buffers_lock_;
   // All buffers, in use or ready to be recycled.
   std::vector<rtc::scoped_refptr<Vp9FrameBuffer>> allocated_buffers_
       GUARDED_BY(buffers_lock_);
-  // If more buffers than this are allocated we print warnings, and crash if
-  // in debug mode.
-  static const size_t max_num_buffers_ = 10;
+  // If more buffers than this are allocated we print warnings and crash if in
+  // debug mode. VP9 is defined to have 8 reference buffers, of which 3 can be
+  // referenced by any frame, see
+  // https://tools.ietf.org/html/draft-grange-vp9-bitstream-00#section-2.2.2.
+  // Assuming VP9 holds on to at most 8 buffers, any more buffers than that
+  // would have to be by application code. Decoded frames should not be
+  // referenced for longer than necessary. If we allow ~60 additional buffers
+  // then the application has ~1 second to e.g. render each frame of a 60 fps
+  // video.
+  static const size_t max_num_buffers_ = 68;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_CODECS_VP9_VP9_FRAME_BUFFER_POOL_H_