Have AudioRendererImpl advance time until it's told to stop.

media/filters/audio_clock.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_AUDIO_CLOCK_H_
 #define MEDIA_FILTERS_AUDIO_CLOCK_H_
 
 #include <deque>
 
 #include "base/time/time.h"
@@ skipping 11 matching lines @@
   ~AudioClock();
 
   // |frames_written| amount of audio data scaled to |playback_rate| written.
   // |frames_requested| amount of audio data requested by hardware.
   // |delay_frames| is the current amount of hardware delay.
   void WroteAudio(int frames_written,
                   int frames_requested,
                   int delay_frames,
                   float playback_rate);
 
-  // Calculates the current media timestamp taking silence and changes in
-  // playback rate into account.
-  base::TimeDelta current_media_timestamp() const {
-    return current_media_timestamp_;
-  }
+  // Returns the bounds of media data currently buffered by the audio hardware,
+  // taking silence and changes in playback rate into account.
+  //

[DaleCurtis, 2014/09/03 22:00:45]

Can you add the WroteAudio() calls that generated this structure? The comment
doesn't explain why the silent frames are not considered for the
back_timestamp().

[scherkus (not reviewing), 2014/09/03 22:23:18]

Done.

+  // start_timestamp = 1000 ms                            sample_rate = 40 Hz
+  // +-----------------------+----------------------+-----------------------+
+  // |   10 frames silence   |   20 frames @ 1.0x   |   20 frames @ 0.5x    |
+  // |                       |       = 500 ms       |       = 250 ms        |
+  // +-----------------------+----------------------+-----------------------+
+  // ^                                                                      ^
+  // front_timestamp() is equal to               back_timestamp() is equal to
+  // |start_timestamp| since no                  amount of media frames tracked
+  // media data has been played yet.             by AudioClock, which would be
+  //                                             1750 ms.
+  base::TimeDelta front_timestamp() const { return front_timestamp_; }
+  base::TimeDelta back_timestamp() const { return back_timestamp_; }
 
   // Clients can provide |time_since_writing| to simulate the passage of time
   // since last writing audio to get a more accurate current media timestamp.
-  base::TimeDelta CurrentMediaTimestampSinceWriting(
+  //
+  // The value will be bounded between front_timestamp() and back_timestamp().
+  base::TimeDelta TimestampSinceWriting(
       base::TimeDelta time_since_writing) const;
 
   // Returns the amount of contiguous media time buffered at the head of the
   // audio hardware buffer. Silence introduced into the audio hardware buffer is
   // treated as a break in media time.
   base::TimeDelta contiguous_audio_data_buffered() const {
     return contiguous_audio_data_buffered_;
   }
 
   // Same as above, but also treats changes in playback rate as a break in media
   // time.
   base::TimeDelta contiguous_audio_data_buffered_at_same_rate() const {
     return contiguous_audio_data_buffered_at_same_rate_;
   }
 
-  // Returns true if there is any audio data buffered by the audio hardware,
-  // even if there is silence mixed in.
-  bool audio_data_buffered() const { return audio_data_buffered_; }
-
  private:
   // Even with a ridiculously high sample rate of 256kHz, using 64 bits will
   // permit tracking up to 416999965 days worth of time (that's 1141 millenia).
   //
   // 32 bits on the other hand would top out at measly 2 hours and 20 minutes.
   struct AudioData {
     AudioData(int64_t frames, float playback_rate);
 
     int64_t frames;
     float playback_rate;
   };
 
   // Helpers for operating on |buffered_|.
   void PushBufferedAudioData(int64_t frames, float playback_rate);
   void PopBufferedAudioData(int64_t frames);
   base::TimeDelta ComputeBufferedMediaTime(int64_t frames) const;
 
   const base::TimeDelta start_timestamp_;
   const int sample_rate_;
   const double microseconds_per_frame_;
 
   std::deque<AudioData> buffered_;
   int64_t total_buffered_frames_;
 
-  base::TimeDelta current_media_timestamp_;
+  base::TimeDelta front_timestamp_;
+  base::TimeDelta back_timestamp_;
 
   // Cached results of last call to WroteAudio().
-  bool audio_data_buffered_;
   base::TimeDelta contiguous_audio_data_buffered_;
   base::TimeDelta contiguous_audio_data_buffered_at_same_rate_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioClock);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_AUDIO_CLOCK_H_