Move ContentVideoCaptureDeviceCore from src/content to src/media

content/browser/media/capture/animated_content_sampler.cc

-// 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.
-
-#include "content/browser/media/capture/animated_content_sampler.h"
-
-#include <algorithm>
-
-namespace content {
-
-namespace {
-
-// These specify the minimum/maximum amount of recent event history to examine
-// to detect animated content.  If the values are too low, there is a greater
-// risk of false-positive detections and low accuracy.  If they are too high,
-// the the implementation will be slow to lock-in/out, and also will not react
-// well to mildly-variable frame rate content (e.g., 25 +/- 1 FPS).
-//
-// These values were established by experimenting with a wide variety of
-// scenarios, including 24/25/30 FPS videos, 60 FPS WebGL demos, and the
-// transitions between static and animated content.
-const int kMinObservationWindowMillis = 1000;
-const int kMaxObservationWindowMillis = 2000;
-
-// The maximum amount of time that can elapse before declaring two subsequent
-// events as "not animating."  This is the same value found in
-// cc::FrameRateCounter.
-const int kNonAnimatingThresholdMillis = 250;  // 4 FPS
-
-// The slowest that content can be animating in order for AnimatedContentSampler
-// to lock-in.  This is the threshold at which the "smoothness" problem is no
-// longer relevant.
-const int kMaxLockInPeriodMicros = 83333;  // 12 FPS
-
-// The amount of time over which to fully correct the drift of the rewritten
-// frame timestamps from the presentation event timestamps.  The lower the
-// value, the higher the variance in frame timestamps.
-const int kDriftCorrectionMillis = 2000;
-
-}  // anonymous namespace
-
-AnimatedContentSampler::AnimatedContentSampler(
-    base::TimeDelta min_capture_period)
-    : min_capture_period_(min_capture_period),
-      sampling_state_(NOT_SAMPLING) {
-  DCHECK_GT(min_capture_period_, base::TimeDelta());
-}
-
-AnimatedContentSampler::~AnimatedContentSampler() {}
-
-void AnimatedContentSampler::SetTargetSamplingPeriod(base::TimeDelta period) {
-  target_sampling_period_ = period;
-}
-
-void AnimatedContentSampler::ConsiderPresentationEvent(
-    const gfx::Rect& damage_rect, base::TimeTicks event_time) {
-  // Analyze the current event and recent history to determine whether animating
-  // content is detected.
-  AddObservation(damage_rect, event_time);
-  if (!AnalyzeObservations(event_time, &detected_region_, &detected_period_) ||
-      detected_period_ <= base::TimeDelta() ||
-      detected_period_ >
-          base::TimeDelta::FromMicroseconds(kMaxLockInPeriodMicros)) {
-    // Animated content not detected.
-    detected_region_ = gfx::Rect();
-    detected_period_ = base::TimeDelta();
-    sampling_state_ = NOT_SAMPLING;
-    return;
-  }
-
-  // At this point, animation is being detected.  Update the sampling period
-  // since the client may call the accessor method even if the heuristics below
-  // decide not to sample the current event.
-  sampling_period_ = ComputeSamplingPeriod(detected_period_,
-                                           target_sampling_period_,
-                                           min_capture_period_);
-
-  // If this is the first event causing animating content to be detected,
-  // transition to the START_SAMPLING state.
-  if (sampling_state_ == NOT_SAMPLING)
-    sampling_state_ = START_SAMPLING;
-
-  // If the current event does not represent a frame that is part of the
-  // animation, do not sample.
-  if (damage_rect != detected_region_) {
-    if (sampling_state_ == SHOULD_SAMPLE)
-      sampling_state_ = SHOULD_NOT_SAMPLE;
-    return;
-  }
-
-  // When starting sampling, determine where to sync-up for sampling and frame
-  // timestamp rewriting.  Otherwise, just add one animation period's worth of
-  // tokens to the token bucket.
-  if (sampling_state_ == START_SAMPLING) {
-    if (event_time - frame_timestamp_ > sampling_period_) {
-      // The frame timestamp sequence should start with the current event
-      // time.
-      frame_timestamp_ = event_time - sampling_period_;
-      token_bucket_ = sampling_period_;
-    } else {
-      // The frame timestamp sequence will continue from the last recorded
-      // frame timestamp.
-      token_bucket_ = event_time - frame_timestamp_;
-    }
-
-    // Provide a little extra in the initial token bucket so that minor error in
-    // the detected period won't prevent a reasonably-timed event from being
-    // sampled.
-    token_bucket_ += detected_period_ / 2;
-  } else {
-    token_bucket_ += detected_period_;
-  }
-
-  // If the token bucket is full enough, take tokens from it and propose
-  // sampling.  Otherwise, do not sample.
-  DCHECK_LE(detected_period_, sampling_period_);
-  if (token_bucket_ >= sampling_period_) {
-    token_bucket_ -= sampling_period_;
-    frame_timestamp_ = ComputeNextFrameTimestamp(event_time);
-    sampling_state_ = SHOULD_SAMPLE;
-  } else {
-    sampling_state_ = SHOULD_NOT_SAMPLE;
-  }
-}
-
-bool AnimatedContentSampler::HasProposal() const {
-  return sampling_state_ != NOT_SAMPLING;
-}
-
-bool AnimatedContentSampler::ShouldSample() const {
-  return sampling_state_ == SHOULD_SAMPLE;
-}
-
-void AnimatedContentSampler::RecordSample(base::TimeTicks frame_timestamp) {
-  if (sampling_state_ == NOT_SAMPLING)
-    frame_timestamp_ = frame_timestamp;
-  else if (sampling_state_ == SHOULD_SAMPLE)
-    sampling_state_ = SHOULD_NOT_SAMPLE;
-}
-
-void AnimatedContentSampler::AddObservation(const gfx::Rect& damage_rect,
-                                            base::TimeTicks event_time) {
-  if (damage_rect.IsEmpty())
-    return;  // Useless observation.
-
-  // Add the observation to the FIFO queue.
-  if (!observations_.empty() && observations_.back().event_time > event_time)
-    return;  // The implementation assumes chronological order.
-  observations_.push_back(Observation(damage_rect, event_time));
-
-  // Prune-out old observations.
-  const base::TimeDelta threshold =
-      base::TimeDelta::FromMilliseconds(kMaxObservationWindowMillis);
-  while ((event_time - observations_.front().event_time) > threshold)
-    observations_.pop_front();
-}
-
-gfx::Rect AnimatedContentSampler::ElectMajorityDamageRect() const {
-  // This is an derivative of the Boyer-Moore Majority Vote Algorithm where each
-  // pixel in a candidate gets one vote, as opposed to each candidate getting
-  // one vote.
-  const gfx::Rect* candidate = NULL;
-  int64 votes = 0;
-  for (ObservationFifo::const_iterator i = observations_.begin();
-       i != observations_.end(); ++i) {
-    DCHECK_GT(i->damage_rect.size().GetArea(), 0);
-    if (votes == 0) {
-      candidate = &(i->damage_rect);
-      votes = candidate->size().GetArea();
-    } else if (i->damage_rect == *candidate) {
-      votes += i->damage_rect.size().GetArea();
-    } else {
-      votes -= i->damage_rect.size().GetArea();
-      if (votes < 0) {
-        candidate = &(i->damage_rect);
-        votes = -votes;
-      }
-    }
-  }
-  return (votes > 0) ? *candidate : gfx::Rect();
-}
-
-bool AnimatedContentSampler::AnalyzeObservations(
-    base::TimeTicks event_time,
-    gfx::Rect* rect,
-    base::TimeDelta* period) const {
-  const gfx::Rect elected_rect = ElectMajorityDamageRect();
-  if (elected_rect.IsEmpty())
-    return false;  // There is no regular animation present.
-
-  // Scan |observations_|, gathering metrics about the ones having a damage Rect
-  // equivalent to the |elected_rect|.  Along the way, break early whenever the
-  // event times reveal a non-animating period.
-  int64 num_pixels_damaged_in_all = 0;
-  int64 num_pixels_damaged_in_chosen = 0;
-  base::TimeDelta sum_frame_durations;
-  size_t count_frame_durations = 0;
-  base::TimeTicks first_event_time;
-  base::TimeTicks last_event_time;
-  for (ObservationFifo::const_reverse_iterator i = observations_.rbegin();
-       i != observations_.rend(); ++i) {
-    const int area = i->damage_rect.size().GetArea();
-    num_pixels_damaged_in_all += area;
-    if (i->damage_rect != elected_rect)
-      continue;
-    num_pixels_damaged_in_chosen += area;
-    if (last_event_time.is_null()) {
-      last_event_time = i->event_time;
-      if ((event_time - last_event_time) >=
-              base::TimeDelta::FromMilliseconds(kNonAnimatingThresholdMillis)) {
-        return false;  // Content animation has recently ended.
-      }
-    } else {
-      const base::TimeDelta frame_duration = first_event_time - i->event_time;
-      if (frame_duration >=
-              base::TimeDelta::FromMilliseconds(kNonAnimatingThresholdMillis)) {
-        break;  // Content not animating before this point.
-      }
-      sum_frame_durations += frame_duration;
-      ++count_frame_durations;
-    }
-    first_event_time = i->event_time;
-  }
-
-  if ((last_event_time - first_event_time) <
-          base::TimeDelta::FromMilliseconds(kMinObservationWindowMillis)) {
-    return false;  // Content has not animated for long enough for accuracy.
-  }
-  if (num_pixels_damaged_in_chosen <= (num_pixels_damaged_in_all * 2 / 3))
-    return false;  // Animation is not damaging a supermajority of pixels.
-
-  *rect = elected_rect;
-  DCHECK_GT(count_frame_durations, 0u);
-  *period = sum_frame_durations / count_frame_durations;
-  return true;
-}
-
-base::TimeTicks AnimatedContentSampler::ComputeNextFrameTimestamp(
-    base::TimeTicks event_time) const {
-  // The ideal next frame timestamp one sampling period since the last one.
-  const base::TimeTicks ideal_timestamp = frame_timestamp_ + sampling_period_;
-
-  // Account for two main sources of drift: 1) The clock drift of the system
-  // clock relative to the video hardware, which affects the event times; and
-  // 2) The small error introduced by this frame timestamp rewriting, as it is
-  // based on averaging over recent events.
-  //
-  // TODO(miu): This is similar to the ClockSmoother in
-  // media/base/audio_shifter.cc.  Consider refactor-and-reuse here.
-  const base::TimeDelta drift = ideal_timestamp - event_time;
-  const int64 correct_over_num_frames =
-      base::TimeDelta::FromMilliseconds(kDriftCorrectionMillis) /
-          sampling_period_;
-  DCHECK_GT(correct_over_num_frames, 0);
-
-  return ideal_timestamp - drift / correct_over_num_frames;
-}
-
-// static
-base::TimeDelta AnimatedContentSampler::ComputeSamplingPeriod(
-      base::TimeDelta animation_period,
-      base::TimeDelta target_sampling_period,
-      base::TimeDelta min_capture_period) {
-  // If the animation rate is unknown, return the ideal sampling period.
-  if (animation_period == base::TimeDelta()) {
-    return std::max(target_sampling_period, min_capture_period);
-  }
-
-  // Determine whether subsampling is needed.  If so, compute the sampling
-  // period corresponding to the sampling rate is the closest integer division
-  // of the animation frame rate to the target sampling rate.
-  //
-  // For example, consider a target sampling rate of 30 FPS and an animation
-  // rate of 42 FPS.  Possible sampling rates would be 42/1 = 42, 42/2 = 21,
-  // 42/3 = 14, and so on.  Of these candidates, 21 FPS is closest to 30.
-  base::TimeDelta sampling_period;
-  if (animation_period < target_sampling_period) {
-    const int64 ratio = target_sampling_period / animation_period;
-    const double target_fps = 1.0 / target_sampling_period.InSecondsF();
-    const double animation_fps = 1.0 / animation_period.InSecondsF();
-    if (std::abs(animation_fps / ratio - target_fps) <
-            std::abs(animation_fps / (ratio + 1) - target_fps)) {
-      sampling_period = ratio * animation_period;
-    } else {
-      sampling_period = (ratio + 1) * animation_period;
-    }
-  } else {
-    sampling_period = animation_period;
-  }
-  return std::max(sampling_period, min_capture_period);
-}
-
-}  // namespace content