Fix ChunkDemuxer seek deadlock

media/base/filters.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.
 
 // Filters are connected in a strongly typed manner, with downstream filters
 // always reading data from upstream filters.  Upstream filters have no clue
 // who is actually reading from them, and return the results via callbacks.
 //
 //                         DemuxerStream(Video) <- VideoDecoder <- VideoRenderer
 // DataSource <- Demuxer <
@@ skipping 117 matching lines @@
   virtual void Initialize(DemuxerStream* stream,
                           const PipelineStatusCB& callback,
                           const StatisticsCallback& stats_callback) = 0;
 
   // Request a frame to be decoded and returned via the provided callback.
   // Only one read may be in flight at any given time.
   //
   // Implementations guarantee that the callback will not be called from within
   // this method.
   //
-  // Frames will be non-NULL yet may be end of stream frames.
+  // Non-NULL frames contain decoded video data or may indicate the  end of
+  // the stream. NULL video frames indicate an aborted read. This can happen if
+  // the DemuxerStream gets flushed and doesn't have any more data to return.
+  // An aborted read indicates a seek will likely happen shortly.

[Ami GONE FROM CHROMIUM, 2012/01/27 23:44:58]

I don't like the "likely" in the last sentence here for an API contract.  Drop
the sentence or convert to something that's a specification?

(ditto for the audio version below)

[acolwell GONE FROM CHROMIUM, 2012/01/29 03:00:41]

Done.

   typedef base::Callback<void(scoped_refptr<VideoFrame>)> ReadCB;
   virtual void Read(const ReadCB& callback) = 0;
 
   // Returns the natural width and height of decoded video in pixels.
   //
   // Clients should NOT rely on these values to remain constant. Instead, use
   // the width/height from decoded video frames themselves.
   //
   // TODO(scherkus): why not rely on prerolling and decoding a single frame to
   // get dimensions?
@@ skipping 27 matching lines @@
   // TODO(scherkus): switch to PipelineStatus callback.
   virtual void Initialize(DemuxerStream* stream, const base::Closure& callback,
                           const StatisticsCallback& stats_callback) = 0;
 
   // Request samples to be decoded and returned via the provided callback.
   // Only one read may be in flight at any given time.
   //
   // Implementations guarantee that the callback will not be called from within
   // this method.
   //
-  // Sample buffers will be non-NULL yet may be end of stream buffers.
+  // Non-NULL sample buffer pointers will contain decoded audio data or may
+  // indicate the end of the stream. A NULL buffer pointer indicates an aborted
+  // Read(). This can happen if the DemuxerStream gets flushed and doesn't have
+  // any more data to return. An aborted read indicates a seek will likely
+  // happen shortly.
   typedef base::Callback<void(scoped_refptr<Buffer>)> ReadCB;
   virtual void Read(const ReadCB& callback) = 0;
 
   // Returns various information about the decoded audio format.
   virtual int bits_per_channel() = 0;
   virtual ChannelLayout channel_layout() = 0;
   virtual int samples_per_second() = 0;
 
  protected:
   AudioDecoder();
@@ skipping 35 matching lines @@
 
   // Resumes playback after underflow occurs.
   // |buffer_more_audio| is set to true if you want to increase the size of the
   // decoded audio buffer.
   virtual void ResumeAfterUnderflow(bool buffer_more_audio) = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_FILTERS_H_