media/capture/smooth_event_sampler.h

   1 // Copyright (c) 2015 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_CAPTURE_SMOOTH_EVENT_SAMPLER_H_
   6 #define MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_
   7
   8 #include "base/time/time.h"
   9 #include "media/base/media_export.h"
  10
  11 namespace media {
  12
  13 // Filters a sequence of events to achieve a target frequency.
  14 class MEDIA_EXPORT SmoothEventSampler {
  15  public:
  16   SmoothEventSampler(base::TimeDelta min_capture_period,
  17                      int redundant_capture_goal);
  18
  19   // Get/Set minimum capture period. When setting a new value, the state of the
  20   // sampler is retained so that sampling will continue smoothly.
  21   base::TimeDelta min_capture_period() const { return min_capture_period_; }
  22   void SetMinCapturePeriod(base::TimeDelta p);
  23
  24   // Add a new event to the event history, and consider whether it ought to be
  25   // sampled. The event is not recorded as a sample until RecordSample() is
  26   // called.
  27   void ConsiderPresentationEvent(base::TimeTicks event_time);
  28
  29   // Returns true if the last event considered should be sampled.
  30   bool ShouldSample() const;
  31
  32   // Operates on the last event added by ConsiderPresentationEvent(), marking
  33   // it as sampled. After this point we are current in the stream of events, as
  34   // we have sampled the most recent event.
  35   void RecordSample();
  36
  37   // Returns true if, at time |event_time|, sampling should occur because too
  38   // much time will have passed relative to the last event and/or sample.
  39   bool IsOverdueForSamplingAt(base::TimeTicks event_time) const;
  40
  41   // Returns true if ConsiderPresentationEvent() has been called since the last
  42   // call to RecordSample().
  43   bool HasUnrecordedEvent() const;
  44
  45  private:
  46   base::TimeDelta min_capture_period_;
  47   const int redundant_capture_goal_;
  48   base::TimeDelta token_bucket_capacity_;
  49
  50   base::TimeTicks current_event_;
  51   base::TimeTicks last_sample_;
  52   int overdue_sample_count_;
  53   base::TimeDelta token_bucket_;
  54
  55   DISALLOW_COPY_AND_ASSIGN(SmoothEventSampler);
  56 };
  57
  58 }  // namespace media
  59
  60 #endif  // MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_