Introduce AudioDiscardHelper. Refactor audio decoders to use it.

media/filters/opus_audio_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_FILTERS_OPUS_AUDIO_DECODER_H_
 #define MEDIA_FILTERS_OPUS_AUDIO_DECODER_H_
 
 #include "base/callback.h"
 #include "base/time/time.h"
 #include "media/base/audio_decoder.h"
 #include "media/base/demuxer_stream.h"
 #include "media/base/sample_format.h"
 
 struct OpusMSDecoder;
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace media {
 
 class AudioBuffer;
-class AudioTimestampHelper;
+class AudioDiscardHelper;
 class DecoderBuffer;
 struct QueuedAudioBuffer;
 
 class MEDIA_EXPORT OpusAudioDecoder : public AudioDecoder {
  public:
   explicit OpusAudioDecoder(
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
   virtual ~OpusAudioDecoder();
 
   // AudioDecoder implementation.
@@ skipping 14 matching lines @@
   void CloseDecoder();
   void ResetTimestampState();
   bool Decode(const scoped_refptr<DecoderBuffer>& input,
               scoped_refptr<AudioBuffer>* output_buffer);
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
   AudioDecoderConfig config_;
   OpusMSDecoder* opus_decoder_;
 
-  // Used for computing output timestamps.
-  scoped_ptr<AudioTimestampHelper> output_timestamp_helper_;
-  base::TimeDelta last_input_timestamp_;
-
-  // Number of frames to be discarded from the start of the packet. This value
-  // is respected for all packets except for the first one in the stream. For
-  // the first packet in the stream, |frame_delay_at_start_| is used. This is
-  // usually set to the SeekPreRoll value from the container whenever a seek
-  // happens.
-  int frames_to_discard_;
-
   // When the input timestamp is |start_input_timestamp_| the decoder needs to
   // drop |config_.codec_delay()| frames.
   base::TimeDelta start_input_timestamp_;
 
+  scoped_ptr<AudioDiscardHelper> discard_helper_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(OpusAudioDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_OPUS_AUDIO_DECODER_H_