Home | History | Annotate | Download | only in media 
      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_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_ORACLE_H_
      6 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_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::Time 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::Time 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::Time current_event_;
     47   base::Time 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(
     74       Event event,
     75       base::Time event_time);
     76 
     77   // Record the start of a capture.  Returns a frame_number to be used with
     78   // CompleteCapture().
     79   int RecordCapture();
     80 
     81   // Record the completion of a capture.  Returns true iff the captured frame
     82   // should be delivered.
     83   bool CompleteCapture(int frame_number, base::Time timestamp);
     84 
     85   base::TimeDelta capture_period() const { return capture_period_; }
     86 
     87  private:
     88 
     89   // Time between frames.
     90   const base::TimeDelta capture_period_;
     91 
     92   // Incremented every time a paint or update event occurs.
     93   int frame_number_;
     94 
     95   // Stores the frame number from the last delivered frame.
     96   int last_delivered_frame_number_;
     97 
     98   // Stores the timestamp of the last delivered frame.
     99   base::Time last_delivered_frame_timestamp_;
    100 
    101   // Tracks present/paint history.
    102   SmoothEventSampler sampler_;
    103 };
    104 
    105 }  // namespace content
    106 
    107 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_ORACLE_H_
    108