blob: 496eced81a4996f63a1162716df651ec27d6a8fc (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
|
// 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_BASE_TIME_SOURCE_H_
#define MEDIA_BASE_TIME_SOURCE_H_
#include <vector>
#include "base/callback.h"
#include "base/time/time.h"
#include "media/base/media_export.h"
namespace media {
// A TimeSource is capable of providing the current media time.
class MEDIA_EXPORT TimeSource {
public:
// Helper alias for converting media timestamps into a wall clock timestamps.
using WallClockTimeCB =
base::Callback<bool(const std::vector<base::TimeDelta>&,
std::vector<base::TimeTicks>*)>;
TimeSource() {}
virtual ~TimeSource() {}
// Signal the time source to start ticking. It is expected that values from
// CurrentMediaTime() will start increasing.
virtual void StartTicking() = 0;
// Signal the time source to stop ticking. It is expected that values from
// CurrentMediaTime() will remain constant.
virtual void StopTicking() = 0;
// Updates the current playback rate. It is expected that values from
// CurrentMediaTime() will eventually reflect the new playback rate (e.g., the
// media time will advance at half speed if the rate was set to 0.5).
virtual void SetPlaybackRate(double playback_rate) = 0;
// Sets the media time to start ticking from. Only valid to call while the
// time source is not ticking.
virtual void SetMediaTime(base::TimeDelta time) = 0;
// Returns the current media timestamp relative to the timestamp set by
// SetMediaTime().
//
// Values returned are intended for informational purposes, such as displaying
// UI with the current minute and second count. While it is guaranteed values
// will never go backwards, the frequency at which they update may be low.
virtual base::TimeDelta CurrentMediaTime() = 0;
// Converts a vector of media timestamps into a vector of wall clock times; if
// the media time is stopped, returns false, otherwise returns true. Even if
// time is stopped, timestamps will be converted.
//
// Passing an empty |media_timestamps| vector will return the last known media
// time as a wall clock time.
//
// Within a single call to GetWallClockTimes() the returned wall clock times
// are a strictly increasing function of the given media times. There is no
// such guarantee between calls though; e.g., playback rate or audio delay may
// change on other threads within the pipeline.
//
// Each timestamp converted from |media_timestamps| will be pushed into
// |wall_clock_times| such that after all timestamps are converted, the two
// vectors are parallel (media_timestamps[i] -> wall_clock_times[i]).
//
// |media_timestamps| values too far ahead of the current media time will
// be converted to an estimated value; as such, these values may go backwards
// in time slightly between calls to GetWallClockTimes().
//
// |media_timestamps| values behind the current media time may be
// significantly incorrect if the playback rate has changed recently. The only
// guarantee is that the returned time will be less than the current wall
// clock time.
virtual bool GetWallClockTimes(
const std::vector<base::TimeDelta>& media_timestamps,
std::vector<base::TimeTicks>* wall_clock_times) = 0;
};
} // namespace media
#endif // MEDIA_BASE_TIME_SOURCE_H_
|
