content/browser/media/capture/video_capture_oracle.h

   1 // Copyright (c) 2013 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 CONTENT_BROWSER_MEDIA_CAPTURE_VIDEO_CAPTURE_ORACLE_H_
   6 #define CONTENT_BROWSER_MEDIA_CAPTURE_VIDEO_CAPTURE_ORACLE_H_
   7
   8 #include "base/callback_forward.h"
   9 #include "base/memory/scoped_ptr.h"
  10 #include "base/time/time.h"
  11 #include "content/common/content_export.h"
  12
  13 namespace content {
  14
  15 // Filters a sequence of events to achieve a target frequency.
  16 class CONTENT_EXPORT SmoothEventSampler {
  17  public:
  18   explicit SmoothEventSampler(base::TimeDelta capture_period,
  19                               bool events_are_reliable,
  20                               int redundant_capture_goal);
  21
  22   // Add a new event to the event history, and return whether it ought to be
  23   // sampled based on the desired |capture_period|. The event is not recorded as
  24   // a sample until RecordSample() is called.
  25   bool AddEventAndConsiderSampling(base::TimeTicks event_time);
  26
  27   // Operates on the last event added by AddEventAndConsiderSampling(), marking
  28   // it as sampled. After this point we are current in the stream of events, as
  29   // we have sampled the most recent event.
  30   void RecordSample();
  31
  32   // Returns true if, at time |event_time|, sampling should occur because too
  33   // much time will have passed relative to the last event and/or sample.
  34   bool IsOverdueForSamplingAt(base::TimeTicks event_time) const;
  35
  36   // Returns true if AddEventAndConsiderSampling() has been called since the
  37   // last call to RecordSample().
  38   bool HasUnrecordedEvent() const;
  39
  40  private:
  41   const bool events_are_reliable_;
  42   const base::TimeDelta capture_period_;
  43   const int redundant_capture_goal_;
  44   const base::TimeDelta token_bucket_capacity_;
  45
  46   base::TimeTicks current_event_;
  47   base::TimeTicks last_sample_;
  48   int overdue_sample_count_;
  49   base::TimeDelta token_bucket_;
  50
  51   DISALLOW_COPY_AND_ASSIGN(SmoothEventSampler);
  52 };
  53
  54 // VideoCaptureOracle manages the producer-side throttling of captured frames
  55 // from a video capture device.  It is informed of every update by the device;
  56 // this empowers it to look into the future and decide if a particular frame
  57 // ought to be captured in order to achieve its target frame rate.
  58 class CONTENT_EXPORT VideoCaptureOracle {
  59  public:
  60   enum Event {
  61     kTimerPoll,
  62     kCompositorUpdate,
  63     kSoftwarePaint,
  64   };
  65
  66   VideoCaptureOracle(base::TimeDelta capture_period,
  67                      bool events_are_reliable);
  68   virtual ~VideoCaptureOracle() {}
  69
  70   // Record an event of type |event|, and decide whether the caller should do a
  71   // frame capture immediately. Decisions of the oracle are final: the caller
  72   // must do what it is told.
  73   bool ObserveEventAndDecideCapture(Event event, base::TimeTicks event_time);
  74
  75   // Record the start of a capture.  Returns a frame_number to be used with
  76   // CompleteCapture().
  77   int RecordCapture();
  78
  79   // Record the completion of a capture.  Returns true iff the captured frame
  80   // should be delivered.
  81   bool CompleteCapture(int frame_number, base::TimeTicks timestamp);
  82
  83   base::TimeDelta capture_period() const { return capture_period_; }
  84
  85  private:
  86
  87   // Time between frames.
  88   const base::TimeDelta capture_period_;
  89
  90   // Incremented every time a paint or update event occurs.
  91   int frame_number_;
  92
  93   // Stores the frame number from the last delivered frame.
  94   int last_delivered_frame_number_;
  95
  96   // Stores the timestamp of the last delivered frame.
  97   base::TimeTicks last_delivered_frame_timestamp_;
  98
  99   // Tracks present/paint history.
 100   SmoothEventSampler sampler_;
 101 };
 102
 103 }  // namespace content
 104
 105 #endif  // CONTENT_BROWSER_MEDIA_CAPTURE_VIDEO_CAPTURE_ORACLE_H_