media/base/time_delta_interpolator.h

   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(double 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   double playback_rate_;
  76
  77   DISALLOW_COPY_AND_ASSIGN(TimeDeltaInterpolator);
  78 };
  79
  80 }  // namespace media
  81
  82 #endif  // MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_