Introduce AudioClock to improve playback delay calculations.

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"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Models a queue of buffered audio in a playback pipeline for use with
+// estimating the amount of delay in wall clock time. Takes changes in playback
+// rate into account to handle scenarios where multiple rates may be present in
+// a playback pipeline with large delay.
+class MEDIA_EXPORT AudioClock {
+ public:
+  explicit AudioClock(int sample_rate);
+  ~AudioClock();
+
+  // |frames| amount of audio data scaled to |playback_rate| was written.
+  // |delay_frames| is the current amount of hardware delay.
+  // |timestamp| is the endpoint media timestamp of the audio data written.
+  void WroteAudio(int frames,
+                  int delay_frames,
+                  float playback_rate,
+                  base::TimeDelta timestamp);
+
+  // |frames| amount of silence was written.
+  // |delay_frames| is the current amount of hardware delay.
+  void WroteSilence(int frames, int delay_frames);

[scherkus (not reviewing), 2014/04/30 19:13:58]

went with two separate APIs as it started to look really funky when writing only
silence as you get forced to provide playback_rate and timestamp

+
+  // Calculates the current media timestamp taking silence and changes in
+  // playback rate into account.
+  base::TimeDelta CurrentMediaTimestamp() const;
+
+  // Returns the last endpoint timestamp provided to WroteAudio().
+  base::TimeDelta LastEndpointTimestamp() const;
+
+ private:
+  void TrimBufferedAudioToMatchDelay(int delay_frames);
+  void PushBufferedAudio(int frames,
+                         float playback_rate,
+                         base::TimeDelta endpoint_timestamp);
+
+  int sample_rate_;

[DaleCurtis, 2014/04/30 20:36:33]

const

[scherkus (not reviewing), 2014/05/02 19:26:05]

Done.

+
+  // Initially set to kNoTimestamp(), otherwise is the last endpoint timestamp
+  // delivered to WroteAudio(). A copy is kept outside of |buffered_audio_| to
+  // handle the case where all of |buffered_audio_| has been replaced with
+  // silence.
+  base::TimeDelta last_endpoint_timestamp_;
+
+  struct BufferedAudio {
+    BufferedAudio(int frames,
+                  float playback_rate,
+                  base::TimeDelta endpoint_timestamp);
+
+    int frames;
+    float playback_rate;

[DaleCurtis, 2014/04/30 20:36:33]

Looks like this could be const?

[scherkus (not reviewing), 2014/05/02 19:26:05]

adding const interferes with the implicit copy operator used when doing
operations on std::deque<BufferedAudio>

+    base::TimeDelta endpoint_timestamp;
+  };
+
+  std::deque<BufferedAudio> buffered_audio_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioClock);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_AUDIO_CLOCK_H_