1// Copyright 2014 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
6#define MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
7
8#include "base/basictypes.h"
9#include "base/time/time.h"
10#include "media/base/media_export.h"
11
12namespace base {
13class TickClock;
14}  // namespace base
15
16namespace media {
17
18// Interpolates between two TimeDeltas based on the passage of wall clock time
19// and the current playback rate.
20//
21// TimeDeltaInterpolator is not thread-safe and must be externally locked.
22class MEDIA_EXPORT TimeDeltaInterpolator {
23 public:
24  // Constructs an interpolator initialized to zero with a rate of 1.0.
25  //
26  // |tick_clock| is used for sampling wall clock time for interpolating.
27  explicit TimeDeltaInterpolator(base::TickClock* tick_clock);
28  ~TimeDeltaInterpolator();
29
30  bool interpolating() { return interpolating_; }
31
32  // Starts returning interpolated TimeDelta values.
33  //
34  // |tick_clock| will be queried for a new reference time value.
35  base::TimeDelta StartInterpolating();
36
37  // Stops returning interpolated TimeDelta values.
38  //
39  // |tick_clock| will be queried for a new reference time value.
40  base::TimeDelta StopInterpolating();
41
42  // Sets a new rate at which to interpolate.
43  //
44  // |tick_clock| will be queried for a new reference time value.
45  void SetPlaybackRate(float playback_rate);
46
47  // Sets the two timestamps to interpolate between at |playback_rate_|.
48  // |upper_bound| must be greater or equal to |lower_bound|.
49  //
50  // |upper_bound| is typically the media timestamp of the last audio frame
51  // buffered by the audio hardware.
52  void SetBounds(base::TimeDelta lower_bound, base::TimeDelta upper_bound);
53
54  // Sets the upper bound used for interpolation. Note that if |upper_bound| is
55  // less than what was previously set via SetTime(), then all future calls
56  // to GetInterpolatedTime() will return |upper_bound|.
57  void SetUpperBound(base::TimeDelta upper_bound);
58
59  // Computes an interpolated time based on SetTime().
60  base::TimeDelta GetInterpolatedTime();
61
62 private:
63  base::TickClock* const tick_clock_;
64
65  bool interpolating_;
66
67  // The range of time to interpolate between.
68  base::TimeDelta lower_bound_;
69  base::TimeDelta upper_bound_;
70
71  // The monotonic system clock time used for interpolating between
72  // |lower_bound_| and |upper_bound_|.
73  base::TimeTicks reference_;
74
75  float playback_rate_;
76
77  DISALLOW_COPY_AND_ASSIGN(TimeDeltaInterpolator);
78};
79
80}  // namespace media
81
82#endif  // MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
83