Tab/Desktop Capture: Use requests instead of timer-based refreshing.

media/capture/content/video_capture_oracle.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 "media/capture/content/video_capture_oracle.h"
 
 #include <algorithm>
 
 #include "base/format_macros.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/strings/stringprintf.h"
 
 namespace media {
 
 namespace {
 
-// This value controls how many redundant, timer-base captures occur when the
-// content is static. Redundantly capturing the same frame allows iterative
-// quality enhancement, and also allows the buffer to fill in "buffered mode".
-//
-// TODO(nick): Controlling this here is a hack and a layering violation, since
-// it's a strategy specific to the WebRTC consumer, and probably just papers
-// over some frame dropping and quality bugs. It should either be controlled at
-// a higher level, or else redundant frame generation should be pushed down
-// further into the WebRTC encoding stack.
-const int kNumRedundantCapturesOfStaticContent = 200;
+// When a non-compositor event arrives after animation has halted, this
+// controls how much time must elapse before deciding to allow a capture.
+const int kAnimationHaltPeriodBeforeOtherSamplingMicros = 250000;
+
+// When estimating frame durations, this is the hard upper-bound on the
+// estimate.
+const int kUpperBoundDurationEstimateMicros = 1000000;  // 1 second
 
 // The half-life of data points provided to the accumulator used when evaluating
 // the recent utilization of the buffer pool.  This value is based on a
 // simulation, and reacts quickly to change to avoid depleting the buffer pool
 // (which would cause hard frame drops).
 const int kBufferUtilizationEvaluationMicros = 200000;  // 0.2 seconds
 
 // The half-life of data points provided to the accumulator used when evaluating
 // the recent resource utilization of the consumer.  The trade-off made here is
 // reaction time versus over-reacting to outlier data points.
@@ skipping 62 matching lines @@
 
 VideoCaptureOracle::VideoCaptureOracle(
     base::TimeDelta min_capture_period,
     const gfx::Size& max_frame_size,
     media::ResolutionChangePolicy resolution_change_policy,
     bool enable_auto_throttling)
     : auto_throttling_enabled_(enable_auto_throttling),
       next_frame_number_(0),
       last_successfully_delivered_frame_number_(-1),
       num_frames_pending_(0),
-      smoothing_sampler_(min_capture_period,
-                         kNumRedundantCapturesOfStaticContent),
+      smoothing_sampler_(min_capture_period),
       content_sampler_(min_capture_period),
       resolution_chooser_(max_frame_size, resolution_change_policy),
       buffer_pool_utilization_(base::TimeDelta::FromMicroseconds(
           kBufferUtilizationEvaluationMicros)),
       estimated_capable_area_(base::TimeDelta::FromMicroseconds(
           kConsumerCapabilityEvaluationMicros)) {
   VLOG(1) << "Auto-throttling is "
           << (auto_throttling_enabled_ ? "enabled." : "disabled.");
 }
 
@@ skipping 36 matching lines @@
           duration_of_next_frame_ = content_sampler_.sampling_period();
         }
         last_time_animation_was_detected_ = event_time;
       } else {
         VLOG_IF(1, had_proposal) << "Content sampler detects animation ended.";
         should_sample = smoothing_sampler_.ShouldSample();
       }
       break;
     }
 
-    case kTimerPoll:
-      // While the timer is firing, only allow a sampling if there are none
-      // currently in-progress.
-      if (num_frames_pending_ == 0)
-        should_sample = smoothing_sampler_.IsOverdueForSamplingAt(event_time);
+    case kActiveRefreshRequest:
+    case kPassiveRefreshRequest:
+    case kMouseCursorUpdate:
+      // Only allow non-compositor samplings when content has not recently been
+      // animating, and only if there are no samplings currently in progress.
+      if (num_frames_pending_ == 0) {
+        if (!content_sampler_.HasProposal() ||
+            ((event_time - last_time_animation_was_detected_).InMicroseconds() >
+             kAnimationHaltPeriodBeforeOtherSamplingMicros)) {
+          smoothing_sampler_.ConsiderPresentationEvent(event_time);
+          should_sample = smoothing_sampler_.ShouldSample();
+        }
+      }
       break;
 
-    case kMouseCursorUpdate:
-      // Only allow a sampling if there are none currently in-progress.
-      if (num_frames_pending_ == 0) {
-        smoothing_sampler_.ConsiderPresentationEvent(event_time);
-        should_sample = smoothing_sampler_.ShouldSample();
-      }
-      break;
     case kNumEvents:
       NOTREACHED();
       break;
   }
 
   if (!should_sample)
     return false;
 
   // If the exact duration of the next frame has not been determined, estimate
   // it using the difference between the current and last frame.
   if (duration_of_next_frame_.is_zero()) {
     if (next_frame_number_ > 0) {
       duration_of_next_frame_ =
           event_time - GetFrameTimestamp(next_frame_number_ - 1);
     }
-    const base::TimeDelta upper_bound = base::TimeDelta::FromMilliseconds(
-        SmoothEventSampler::OVERDUE_DIRTY_THRESHOLD_MILLIS);
+    const base::TimeDelta upper_bound =
+        base::TimeDelta::FromMilliseconds(kUpperBoundDurationEstimateMicros);
     duration_of_next_frame_ =
         std::max(std::min(duration_of_next_frame_, upper_bound),
                  smoothing_sampler_.min_capture_period());
   }
 
   // Update |capture_size_| and reset all feedback signal accumulators if
   // either: 1) this is the first frame; or 2) |resolution_chooser_| has an
   // updated capture size and sufficient time has passed since the last size
   // change.
   if (next_frame_number_ == 0) {
@@ skipping 125 matching lines @@
   // Translate the utilization metric to be in terms of the capable frame area
   // and update the feedback accumulators.  Research suggests utilization is at
   // most linearly proportional to area, and typically is sublinear.  Either
   // way, the end-to-end system should converge to the right place using the
   // more-conservative assumption (linear).
   const int area_at_full_utilization =
       base::saturated_cast<int>(capture_size_.GetArea() / resource_utilization);
   estimated_capable_area_.Update(area_at_full_utilization, timestamp);
 }
 
+// static
+const char* VideoCaptureOracle::EventAsString(Event event) {
+  switch (event) {
+    case kCompositorUpdate:
+      return "compositor";
+    case kActiveRefreshRequest:
+      return "active_refresh";
+    case kPassiveRefreshRequest:
+      return "passive_refresh";
+    case kMouseCursorUpdate:
+      return "mouse";
+    case kNumEvents:
+      break;
+  }
+  NOTREACHED();
+  return "unknown";
+}
+
 base::TimeTicks VideoCaptureOracle::GetFrameTimestamp(int frame_number) const {
   DCHECK(IsFrameInRecentHistory(frame_number));
   return frame_timestamps_[frame_number % kMaxFrameTimestamps];
 }
 
 void VideoCaptureOracle::SetFrameTimestamp(int frame_number,
                                            base::TimeTicks timestamp) {
   DCHECK(IsFrameInRecentHistory(frame_number));
   frame_timestamps_[frame_number % kMaxFrameTimestamps] = timestamp;
 }
@@ skipping 180 matching lines @@
   // Content is not animating, so permit an immediate increase in the capture
   // area.  This allows the system to quickly improve the quality of
   // non-animating content (frame drops are not much of a concern).
   VLOG(2) << "Proposing a "
           << (100.0 * (increased_area - current_area) / current_area)
           << "% increase in capture area for non-animating content.  :-)";
   return increased_area;
 }
 
 }  // namespace media