1 // Copyright (c) 2012 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_CLOCK_H_ 6 #define MEDIA_BASE_CLOCK_H_ 7 8 #include "base/basictypes.h" 9 #include "base/time/time.h" 10 #include "media/base/media_export.h" 11 12 namespace base { 13 class TickClock; 14 } // namespace base 15 16 namespace media { 17 18 // A clock represents a single source of time to allow audio and video streams 19 // to synchronize with each other. Clock essentially tracks the media time with 20 // respect to some other source of time, whether that may be the monotonic 21 // system clock or updates via SetTime(). Clock uses linear interpolation to 22 // calculate the current media time since the last time SetTime() was called. 23 // 24 // Clocks start off paused with a playback rate of 1.0f and a media time of 0. 25 // 26 // Clock is not thread-safe and must be externally locked. 27 // 28 // TODO(scherkus): Clock will some day be responsible for executing callbacks 29 // given a media time. This will be used primarily by video renderers. For now 30 // we'll keep using a poll-and-sleep solution. 31 // 32 // TODO(miu): Rename media::Clock to avoid confusion (and tripping up the media 33 // PRESUBMIT script on future changes). 34 class MEDIA_EXPORT Clock { 35 public: 36 explicit Clock(base::TickClock* clock); 37 ~Clock(); 38 39 // Returns true if the clock is running. 40 bool IsPlaying() const; 41 42 // Starts the clock and returns the current media time, which will increase 43 // with respect to the current playback rate. 44 base::TimeDelta Play(); 45 46 // Stops the clock and returns the current media time, which will remain 47 // constant until Play() is called. 48 base::TimeDelta Pause(); 49 50 // Sets a new playback rate. The rate at which the media time will increase 51 // will now change. 52 void SetPlaybackRate(float playback_rate); 53 54 // Forcefully sets the media time to |current_time|. The second parameter is 55 // the |max_time| that the clock should progress after a call to Play(). This 56 // value is often the time of the end of the last frame buffered and decoded. 57 // 58 // These values are clamped to the duration of the video, which is initially 59 // set to 0 (before SetDuration() is called). 60 void SetTime(base::TimeDelta current_time, base::TimeDelta max_time); 61 62 // Sets the |max_time| to be returned by a call to Elapsed(). 63 void SetMaxTime(base::TimeDelta max_time); 64 65 // Returns the current elapsed media time. Returns 0 if SetDuration() has 66 // never been called. 67 base::TimeDelta Elapsed(); 68 69 // Sets the duration of the video. Clock expects the duration will be set 70 // exactly once. 71 void SetDuration(base::TimeDelta duration); 72 73 // Returns the duration of the clock, or 0 if not set. 74 base::TimeDelta Duration() const; 75 76 private: 77 // Updates the reference points based on the current calculated time. 78 void UpdateReferencePoints(); 79 80 // Updates the reference points based on the given |current_time|. 81 void UpdateReferencePoints(base::TimeDelta current_time); 82 83 // Returns the time elapsed based on the current reference points, ignoring 84 // the |max_time_| cap. 85 base::TimeDelta EstimatedElapsedTime(); 86 87 // Translates |time| into the current media time, based on the perspective of 88 // the monotonically-increasing system clock. 89 base::TimeDelta ElapsedViaProvidedTime(const base::TimeTicks& time) const; 90 91 base::TimeDelta ClampToValidTimeRange(base::TimeDelta time) const; 92 93 base::TickClock* const clock_; 94 95 // Whether the clock is running. 96 bool playing_; 97 98 // Whether the clock is stalled because it has reached the |max_time_| 99 // allowed. 100 bool underflow_; 101 102 // The monotonic system clock time when this Clock last started playing or had 103 // its time set via SetTime(). 104 base::TimeTicks reference_; 105 106 // Current accumulated amount of media time. The remaining portion must be 107 // calculated by comparing the system time to the reference time. 108 base::TimeDelta media_time_; 109 110 // Current playback rate. 111 float playback_rate_; 112 113 // The maximum time that can be returned by calls to Elapsed(). 114 base::TimeDelta max_time_; 115 116 // Duration of the media. 117 base::TimeDelta duration_; 118 119 DISALLOW_COPY_AND_ASSIGN(Clock); 120 }; 121 122 } // namespace media 123 124 #endif // MEDIA_BASE_CLOCK_H_ 125
