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/browser/media/capture/animated_content_sampler.h"
  12 #include "content/browser/media/capture/smooth_event_sampler.h"
  13 #include "content/common/content_export.h"
  14 #include "ui/gfx/geometry/rect.h"
  15
  16 namespace content {
  17
  18 // VideoCaptureOracle manages the producer-side throttling of captured frames
  19 // from a video capture device.  It is informed of every update by the device;
  20 // this empowers it to look into the future and decide if a particular frame
  21 // ought to be captured in order to achieve its target frame rate.
  22 class CONTENT_EXPORT VideoCaptureOracle {
  23  public:
  24   enum Event {
  25     kTimerPoll,
  26     kCompositorUpdate,
  27     kNumEvents,
  28   };
  29
  30   explicit VideoCaptureOracle(base::TimeDelta min_capture_period);
  31   virtual ~VideoCaptureOracle();
  32
  33   // Record a event of type |event|, and decide whether the caller should do a
  34   // frame capture.  |damage_rect| is the region of a frame about to be drawn,
  35   // and may be an empty Rect, if this is not known.  If the caller accepts the
  36   // oracle's proposal, it should call RecordCapture() to indicate this.
  37   bool ObserveEventAndDecideCapture(Event event,
  38                                     const gfx::Rect& damage_rect,
  39                                     base::TimeTicks event_time);
  40
  41   // Record the start of a capture.  Returns a frame_number to be used with
  42   // CompleteCapture().
  43   int RecordCapture();
  44
  45   // Notify of the completion of a capture.  Returns true iff the captured frame
  46   // should be delivered.  |frame_timestamp| is set to the timestamp that should
  47   // be provided to the consumer of the frame.
  48   bool CompleteCapture(int frame_number, base::TimeTicks* frame_timestamp);
  49
  50   base::TimeDelta min_capture_period() const {
  51     return smoothing_sampler_.min_capture_period();
  52   }
  53
  54  private:
  55   // Retrieve/Assign a frame timestamp by capture |frame_number|.
  56   base::TimeTicks GetFrameTimestamp(int frame_number) const;
  57   void SetFrameTimestamp(int frame_number, base::TimeTicks timestamp);
  58
  59   // Incremented every time a paint or update event occurs.
  60   int frame_number_;
  61
  62   // Stores the last |event_time| from the last observation/decision.  Used to
  63   // sanity-check that event times are monotonically non-decreasing.
  64   base::TimeTicks last_event_time_[kNumEvents];
  65
  66   // Stores the frame number from the last delivered frame.
  67   int last_delivered_frame_number_;
  68
  69   // These track present/paint history and propose whether to sample each event
  70   // for capture.  |smoothing_sampler_| uses a "works for all" heuristic, while
  71   // |content_sampler_| specifically detects animated content (e.g., video
  72   // playback) and decides which events to sample to "lock into" that content.
  73   SmoothEventSampler smoothing_sampler_;
  74   AnimatedContentSampler content_sampler_;
  75
  76   // Recent history of frame timestamps proposed by VideoCaptureOracle.  This is
  77   // a ring-buffer, and should only be accessed by the Get/SetFrameTimestamp()
  78   // methods.
  79   enum { kMaxFrameTimestamps = 16 };
  80   base::TimeTicks frame_timestamps_[kMaxFrameTimestamps];
  81 };
  82
  83 }  // namespace content
  84
  85 #endif  // CONTENT_BROWSER_MEDIA_CAPTURE_VIDEO_CAPTURE_ORACLE_H_