Report VideoDecoder status through ReadCB instead of through FilterHost.

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 89 matching lines @@
   virtual ~Filter();
 
   FilterHost* host() const { return host_; }
 
  private:
   FilterHost* host_;
 
   DISALLOW_COPY_AND_ASSIGN(Filter);
 };
 
 class MEDIA_EXPORT VideoDecoder : public Filter {

[Ami GONE FROM CHROMIUM, 2012/04/27 16:49:14]

Can you override Filter::set_host() here to LOG(FATAL) to ensure all callers
have been caught?
(with a TODO pointing at the "make a VideoDecoder not a Filter" crbug saying the
override should be removed when this class stops being a Filter).

[xhwang, 2012/04/27 23:22:30]

Done.

  public:
+  // Status codes for read operations on VideoDecoder.
+  enum Status {
+    kOk,  // Everything went as planned.
+    kDecodeError,  // Decoding error happened.
+    kDecryptError  // Decrypting error happened.
+  };
+
   // Initialize a VideoDecoder with the given DemuxerStream, executing the
   // callback upon completion.
   // statistics_cb is used to update global pipeline statistics.
   virtual void Initialize(DemuxerStream* stream,
                           const PipelineStatusCB& status_cb,
                           const StatisticsCB& statistics_cb) = 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.
   //
   // 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.
-  typedef base::Callback<void(scoped_refptr<VideoFrame>)> ReadCB;
+  typedef base::Callback<void(scoped_refptr<VideoFrame>, Status)> ReadCB;

[Ami GONE FROM CHROMIUM, 2012/04/27 16:49:14]

Typically dependent args follow their dependencies, so I'd make Status the first
param, not second.

[scherkus (not reviewing), 2012/04/27 18:27:56]

Building on top of that -- the docs should be updated to mention what to expect
of VideoFrame given the value of Status

[xhwang, 2012/04/27 23:22:30]

Done.

[xhwang, 2012/04/27 23:22:30]

Done.

   virtual void Read(const ReadCB& read_cb) = 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?
   virtual const gfx::Size& natural_size() = 0;
@@ skipping 71 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_