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_SOURCE_H_ 6 #define MEDIA_BASE_TIME_SOURCE_H_ 7 8 #include "base/time/time.h" 9 #include "media/base/media_export.h" 10 11 namespace media { 12 13 // A TimeSource is capable of providing the current media time. 14 class MEDIA_EXPORT TimeSource { 15 public: 16 TimeSource() {} 17 virtual ~TimeSource() {} 18 19 // Signal the time source to start ticking. It is expected that values from 20 // CurrentMediaTime() will start increasing. 21 virtual void StartTicking() = 0; 22 23 // Signal the time source to stop ticking. It is expected that values from 24 // CurrentMediaTime() will remain constant. 25 virtual void StopTicking() = 0; 26 27 // Updates the current playback rate. It is expected that values from 28 // CurrentMediaTime() will eventually reflect the new playback rate (e.g., the 29 // media time will advance at half speed if the rate was set to 0.5f). 30 virtual void SetPlaybackRate(float playback_rate) = 0; 31 32 // Sets the media time to start ticking from. Only valid to call while the 33 // time source is not ticking. 34 virtual void SetMediaTime(base::TimeDelta time) = 0; 35 36 // Returns the current media time. 37 // 38 // Values returned are intended for informational purposes, such as displaying 39 // UI with the current minute and second count. While it is guaranteed values 40 // will never go backwards, the frequency at which they update may be low. 41 virtual base::TimeDelta CurrentMediaTime() = 0; 42 43 // Returns the current media time for use with synchronizing video. 44 // 45 // Differences from CurrentMediaTime(): 46 // - Values returned update at a much higher frequency (e.g., suitable for 47 // playback of 60 FPS content). 48 // - As a result, values may go slightly backwards depending on the 49 // implementation (e.g., uses interpolation). 50 // 51 // TODO(scherkus): Replace with a method that returns wall clock time for a 52 // given media time for use with VideoFrameScheduler http://crbug.com/110814 53 virtual base::TimeDelta CurrentMediaTimeForSyncingVideo() = 0; 54 }; 55 56 } // namespace media 57 58 #endif // MEDIA_BASE_TIME_SOURCE_H_ 59
