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- // Copyright (c) 2015 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #ifndef MEDIA_CAPTURE_CONTENT_ANIMATED_CONTENT_SAMPLER_H_
- #define MEDIA_CAPTURE_CONTENT_ANIMATED_CONTENT_SAMPLER_H_
- #include "base/containers/circular_deque.h"
- #include "base/time/time.h"
- #include "media/capture/capture_export.h"
- #include "ui/gfx/geometry/rect.h"
- namespace media {
- // Analyzes a sequence of events to detect the presence of constant frame rate
- // animated content. In the case where there are multiple regions of animated
- // content, AnimatedContentSampler will propose sampling the one having the
- // largest "smoothness" impact, according to human perception (e.g., a 24 FPS
- // video versus a 60 FPS busy spinner).
- //
- // In addition, AnimatedContentSampler will provide rewritten frame timestamps,
- // for downstream consumers, that are "truer" to the source content than to the
- // local presentation hardware.
- class CAPTURE_EXPORT AnimatedContentSampler {
- public:
- explicit AnimatedContentSampler(base::TimeDelta min_capture_period);
- ~AnimatedContentSampler();
- // Sets a new minimum capture period.
- void SetMinCapturePeriod(base::TimeDelta period);
- // Get/Set the target sampling period. This is used to determine whether to
- // subsample the frames of animated content.
- base::TimeDelta target_sampling_period() const {
- return target_sampling_period_;
- }
- void SetTargetSamplingPeriod(base::TimeDelta period);
- // Examines the given presentation event metadata, along with recent history,
- // to detect animated content, updating the state of this sampler.
- // |damage_rect| is the region of a frame about to be drawn, while
- // |event_time| refers to the frame's estimated presentation time.
- void ConsiderPresentationEvent(const gfx::Rect& damage_rect,
- base::TimeTicks event_time);
- // Returns true if animated content has been detected and a decision has been
- // made about whether to sample the last event.
- bool HasProposal() const;
- // Returns true if the last event considered should be sampled.
- bool ShouldSample() const;
- // Returns a frame timestamp to provide to consumers of the sampled frame.
- // Only valid when ShouldSample() returns true.
- base::TimeTicks frame_timestamp() const { return frame_timestamp_; }
- // Returns the current sampling period. This can be treated as the estimated
- // duration of the frame to be sampled. Only valid when HasProposal()
- // returns true.
- base::TimeDelta sampling_period() const { return sampling_period_; }
- // Accessors to currently-detected animating region/period, for logging.
- const gfx::Rect& detected_region() const { return detected_region_; }
- base::TimeDelta detected_period() const { return detected_period_; }
- // Records that a frame with the given |frame_timestamp| was sampled. This
- // method should be called when *any* sampling is taken, even if it was not
- // proposed by AnimatedContentSampler.
- void RecordSample(base::TimeTicks frame_timestamp);
- private:
- friend class AnimatedContentSamplerTest;
- // Data structure for efficient online analysis of recent event history.
- struct Observation {
- gfx::Rect damage_rect;
- base::TimeTicks event_time;
- Observation(const gfx::Rect& d, base::TimeTicks e)
- : damage_rect(d), event_time(e) {}
- };
- using ObservationFifo = base::circular_deque<Observation>;
- // Adds an observation to |observations_|, and prunes-out the old ones.
- void AddObservation(const gfx::Rect& damage_rect, base::TimeTicks event_time);
- // Returns the damage Rect that is responsible for the majority of the pixel
- // damage in recent event history, if there is such a Rect. If there isn't,
- // this method could still return any Rect, so the caller must confirm the
- // returned Rect really is responsible for the majority of pixel damage.
- gfx::Rect ElectMajorityDamageRect() const;
- // Analyzes the observations relative to the current |event_time| to detect
- // stable animating content. If detected, returns true and sets the output
- // arguments to the region of the animating content and its mean frame
- // duration.
- bool AnalyzeObservations(base::TimeTicks event_time,
- gfx::Rect* rect,
- base::TimeDelta* period) const;
- // Called by ConsiderPresentationEvent() when the current event is part of a
- // detected animation, to update |frame_timestamp_|.
- base::TimeTicks ComputeNextFrameTimestamp(base::TimeTicks event_time) const;
- // When the animation frame rate is greater than the target sampling rate,
- // this function determines an integer division of the animation frame rate
- // that is closest to the target sampling rate. Returns the inverse of that
- // result (the period). If the animation frame rate is slower or the same as
- // the target sampling rate, this function just returns |animation_period|.
- static base::TimeDelta ComputeSamplingPeriod(
- base::TimeDelta animation_period,
- base::TimeDelta target_sampling_period,
- base::TimeDelta min_capture_period);
- // The client expects frame timestamps to be at least this far apart.
- base::TimeDelta min_capture_period_;
- // A recent history of observations in chronological order, maintained by
- // AddObservation().
- ObservationFifo observations_;
- // The region of currently-detected animated content. If empty, that means
- // "not detected."
- gfx::Rect detected_region_;
- // The mean frame duration of currently-detected animated content. If zero,
- // that means "not detected."
- base::TimeDelta detected_period_;
- // Target period between sampled frames. This can be changed by the client at
- // any time (e.g., to sample high frame rate content at a lower rate).
- base::TimeDelta target_sampling_period_;
- // The sampling period computed during the last call to
- // ConsiderPresentationEvent().
- base::TimeDelta sampling_period_;
- // Indicates whether the last event caused animated content to be detected and
- // whether the current event should be sampled.
- enum {
- NOT_SAMPLING,
- START_SAMPLING,
- SHOULD_NOT_SAMPLE,
- SHOULD_SAMPLE
- } sampling_state_;
- // A token bucket that is used to decide which subset of the frames containing
- // the animated content should be sampled. Here, the smallest discrete unit
- // of time (one microsecond) equals one token; and, tokens are only taken from
- // the bucket when at least a full sampling period's worth are present.
- base::TimeDelta token_bucket_;
- // The rewritten frame timestamp for the latest event.
- base::TimeTicks frame_timestamp_;
- };
- } // namespace media
- #endif // MEDIA_CAPTURE_CONTENT_ANIMATED_CONTENT_SAMPLER_H_
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