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 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(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
