Refactor FFmpegAudioDecoder output timestamp logic.

media/filters/ffmpeg_audio_decoder.h

Index: media/filters/ffmpeg_audio_decoder.h
diff --git a/media/filters/ffmpeg_audio_decoder.h b/media/filters/ffmpeg_audio_decoder.h
index 46af8f0b2340160d2378d512da9c8f2e6ae95522..c63edaed5ef76a1bccb8cf14a67cdd512bad893f 100644
--- a/media/filters/ffmpeg_audio_decoder.h
+++ b/media/filters/ffmpeg_audio_decoder.h
@@ -52,13 +52,10 @@ class MEDIA_EXPORT FFmpegAudioDecoder : public AudioDecoder {
   void DecodeBuffer(DemuxerStream::Status status,
                     const scoped_refptr<DecoderBuffer>& buffer);
 
-  // Updates the output buffer's duration and timestamp based on the input
-  // buffer. Will fall back to an estimated timestamp if the input lacks a
-  // valid timestamp.
-  void UpdateDurationAndTimestamp(const Buffer* input, DataBuffer* output);
-
-  // Calculates duration based on size of decoded audio bytes.
-  base::TimeDelta CalculateDuration(int size);
+  // Returns the timestamp that should be used for the next buffer returned
+  // via |read_cb_|. It is calculated from |output_timestamp_base_| and
+  // |total_frames_decoded_|.
+  base::TimeDelta GetNextOutputTimestamp() const;
 
   // This is !is_null() iff Initialize() hasn't been called.
   base::Callback<MessageLoop*()> message_loop_factory_cb_;
@@ -73,7 +70,15 @@ class MEDIA_EXPORT FFmpegAudioDecoder : public AudioDecoder {
   ChannelLayout channel_layout_;
   int samples_per_second_;
 
-  base::TimeDelta estimated_next_timestamp_;
+  // Used for computing output timestamps.
+  int bytes_per_frame_;
+  base::TimeDelta output_timestamp_base_;
+  double total_frames_decoded_;
+  base::TimeDelta last_input_timestamp_;
+
+  // Number of output sample bytes to drop before generating
+  // output buffers.
+  int output_bytes_to_drop_;
 
   // Holds decoded audio.
   AVFrame* av_frame_;