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/macros.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 // 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. 22 class 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(const base::TickClock* tick_clock); 28 ~TimeDeltaInterpolator(); 29 interpolating()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 // The default rate is 0. 44 // 45 // |tick_clock| will be queried for a new reference time value. 46 void SetPlaybackRate(double playback_rate); 47 48 // Sets the two timestamps to interpolate between at |playback_rate_|. 49 // |upper_bound| must be greater or equal to |lower_bound|. 50 // 51 // |upper_bound| is typically the media timestamp of the last audio frame 52 // buffered by the audio hardware. 53 void SetBounds(base::TimeDelta lower_bound, 54 base::TimeDelta upper_bound, 55 base::TimeTicks capture_time); 56 57 // Sets the upper bound used for interpolation. Note that if |upper_bound| is 58 // less than what was previously set via SetTime(), then all future calls 59 // to GetInterpolatedTime() will return |upper_bound|. 60 void SetUpperBound(base::TimeDelta upper_bound); 61 62 // Computes an interpolated time based on SetTime(). 63 base::TimeDelta GetInterpolatedTime(); 64 65 private: 66 const base::TickClock* const tick_clock_; 67 68 bool interpolating_; 69 70 // The range of time to interpolate between. 71 base::TimeDelta lower_bound_; 72 base::TimeDelta upper_bound_; 73 74 // The monotonic system clock time used for interpolating between 75 // |lower_bound_| and |upper_bound_|. 76 base::TimeTicks reference_; 77 78 double playback_rate_; 79 80 DISALLOW_COPY_AND_ASSIGN(TimeDeltaInterpolator); 81 }; 82 83 } // namespace media 84 85 #endif // MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_ 86