Document purpose of low_delay flag in VideoDecoder interface.

media/base/video_decoder.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_VIDEO_DECODER_H_
 #define MEDIA_BASE_VIDEO_DECODER_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 37 matching lines @@
   // depends on |this|.
   virtual ~VideoDecoder();
 
   // Returns the name of the decoder for logging purpose.
   virtual std::string GetDisplayName() const = 0;
 
   // Initializes a VideoDecoder with the given |config|, executing the
   // |status_cb| upon completion. |output_cb| is called for each output frame
   // decoded by Decode().
   //
+  // If |low_delay| is true then the decoder is not allowed to queue frames,
+  // except for out-of-order frames, i.e. if the next frame can be returned it
+  // must be returned without waiting for Decode() to be called again.
+  // Initialization should fail if |low_delay| is true and the decoder cannot
+  // satisfy the requirements above.
+  //
   // Note:
   // 1) The VideoDecoder will be reinitialized if it was initialized before.
   //    Upon reinitialization, all internal buffered frames will be dropped.
   // 2) This method should not be called during pending decode or reset.
   // 3) No VideoDecoder calls should be made before |status_cb| is executed.
   virtual void Initialize(const VideoDecoderConfig& config,
                           bool low_delay,
                           const PipelineStatusCB& status_cb,
                           const OutputCB& output_cb) = 0;
 
@@ skipping 37 matching lines @@
   // Returns maximum number of parallel decode requests.
   virtual int GetMaxDecodeRequests() const;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(VideoDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_DECODER_H_