media: Support better decoder switching

media/filters/decoder_stream.h

 // Copyright 2014 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_FILTERS_DECODER_STREAM_H_
 #define MEDIA_FILTERS_DECODER_STREAM_H_
 
 #include <deque>
 #include <list>
 #include <memory>
@@ skipping 32 matching lines @@
   typedef typename StreamTraits::DecoderType Decoder;
   typedef typename StreamTraits::OutputType Output;
 
   enum Status {
     OK,  // Everything went as planned.
     ABORTED,  // Read aborted due to Reset() during pending read.
     DEMUXER_READ_ABORTED,  // Demuxer returned aborted read.
     DECODE_ERROR,  // Decoder returned decode error.
   };
 
+  // Callback to create a list of decoders.
+  using CreateDecodersCB = base::RepeatingCallback<ScopedVector<Decoder>()>;
+
   // Indicates completion of a DecoderStream initialization.
-  typedef base::Callback<void(bool success)> InitCB;
+  using InitCB = base::Callback<void(bool success)>;
 
   // Indicates completion of a DecoderStream read.
-  typedef base::Callback<void(Status, const scoped_refptr<Output>&)> ReadCB;
+  using ReadCB = base::Callback<void(Status, const scoped_refptr<Output>&)>;
 
   DecoderStream(const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-                ScopedVector<Decoder> decoders,
+                CreateDecodersCB create_decoders_cb,
                 MediaLog* media_log);
   virtual ~DecoderStream();
 
   // Returns the string representation of the StreamType for logging purpose.
   std::string GetStreamTypeString();
 
   // Initializes the DecoderStream and returns the initialization result
   // through |init_cb|. Note that |init_cb| is always called asynchronously.
   // |cdm_context| can be used to handle encrypted stream. Can be null if the
   // stream is not encrypted.
@@ skipping 133 matching lines @@
 
   CdmContext* cdm_context_;
 
   std::unique_ptr<DecoderSelector<StreamType>> decoder_selector_;
 
   std::unique_ptr<Decoder> decoder_;
 
   // Whether |decoder_| has produced a frame yet. Reset on fallback.
   bool decoder_produced_a_frame_;
 
+  // Whether we are on a fallback decoder. Used to make sure we at most fallback

[watk, 2017/05/04 21:35:33]

What about instead of "on a fallback decoder" we say "using a fallback decoder"?
s/is_on_fallback_decoder_/using_fallback_decoder_/

s/we at most fallback once/we fall back once at most/

I think this is also a confusing name because after the fallback decoder
produces a frame we reset it to false. But it's still a fallback decoder? 

[xhwang, 2017/05/04 23:53:14]

How about has_fallen_back_once_on_decode_error_ ?

I choose this name to make sure we are talking about fallback on decode error,
not reinit error.

Also, I dropped the resetting code. Previously I thought we call fallback on
decode error again after reinit, but it's not the case (controlled by
decoder_produced_a_frame_). We can revisit this later. I have a TODO in the test
about this.

+  // once, to prevent issues like fallback infinitely.

[watk, 2017/05/04 21:35:33]

s/fallback infinitely/infinite fallback/

[xhwang, 2017/05/04 23:53:14]

Done.

+  bool is_on_fallback_decoder_;
+
   std::unique_ptr<DecryptingDemuxerStream> decrypting_demuxer_stream_;
 
   ConfigChangeObserverCB config_change_observer_cb_;
   DecoderChangeObserverCB decoder_change_observer_cb_;
 
   // An end-of-stream buffer has been sent for decoding, no more buffers should
   // be sent for decoding until it completes.
   // TODO(sandersd): Turn this into a State. http://crbug.com/408316
   bool decoding_eos_;
 
@@ skipping 37 matching lines @@
 
 template <>
 int DecoderStream<DemuxerStream::AUDIO>::GetMaxDecodeRequests() const;
 
 typedef DecoderStream<DemuxerStream::VIDEO> VideoFrameStream;
 typedef DecoderStream<DemuxerStream::AUDIO> AudioBufferStream;
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_DECODER_STREAM_H_