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 #include "content/browser/media/capture/video_capture_oracle.h" 6 7 #include "base/debug/trace_event.h" 8 9 namespace content { 10 11 namespace { 12 13 // This value controls how many redundant, timer-base captures occur when the 14 // content is static. Redundantly capturing the same frame allows iterative 15 // quality enhancement, and also allows the buffer to fill in "buffered mode". 16 // 17 // TODO(nick): Controlling this here is a hack and a layering violation, since 18 // it's a strategy specific to the WebRTC consumer, and probably just papers 19 // over some frame dropping and quality bugs. It should either be controlled at 20 // a higher level, or else redundant frame generation should be pushed down 21 // further into the WebRTC encoding stack. 22 const int kNumRedundantCapturesOfStaticContent = 200; 23 24 } // anonymous namespace 25 26 VideoCaptureOracle::VideoCaptureOracle(base::TimeDelta capture_period, 27 bool events_are_reliable) 28 : capture_period_(capture_period), 29 frame_number_(0), 30 last_delivered_frame_number_(0), 31 sampler_(capture_period_, 32 events_are_reliable, 33 kNumRedundantCapturesOfStaticContent) {} 34 35 bool VideoCaptureOracle::ObserveEventAndDecideCapture( 36 Event event, 37 base::TimeTicks event_time) { 38 // Record |event| and decide whether it's a good time to capture. 39 const bool content_is_dirty = (event == kCompositorUpdate || 40 event == kSoftwarePaint); 41 bool should_sample; 42 if (content_is_dirty) { 43 frame_number_++; 44 should_sample = sampler_.AddEventAndConsiderSampling(event_time); 45 } else { 46 should_sample = sampler_.IsOverdueForSamplingAt(event_time); 47 } 48 return should_sample; 49 } 50 51 int VideoCaptureOracle::RecordCapture() { 52 sampler_.RecordSample(); 53 return frame_number_; 54 } 55 56 bool VideoCaptureOracle::CompleteCapture(int frame_number, 57 base::TimeTicks timestamp) { 58 // Drop frame if previous frame number is higher or we're trying to deliver 59 // a frame with the same timestamp. 60 if (last_delivered_frame_number_ > frame_number || 61 last_delivered_frame_timestamp_ == timestamp) { 62 LOG(ERROR) << "Frame with same timestamp or out of order delivery. " 63 << "Dropping frame."; 64 return false; 65 } 66 67 if (last_delivered_frame_timestamp_ > timestamp) { 68 // We should not get here unless time was adjusted backwards. 69 LOG(ERROR) << "Frame with past timestamp (" << timestamp.ToInternalValue() 70 << ") was delivered"; 71 } 72 73 last_delivered_frame_number_ = frame_number; 74 last_delivered_frame_timestamp_ = timestamp; 75 76 return true; 77 } 78 79 SmoothEventSampler::SmoothEventSampler(base::TimeDelta capture_period, 80 bool events_are_reliable, 81 int redundant_capture_goal) 82 : events_are_reliable_(events_are_reliable), 83 capture_period_(capture_period), 84 redundant_capture_goal_(redundant_capture_goal), 85 token_bucket_capacity_(capture_period + capture_period / 2), 86 overdue_sample_count_(0), 87 token_bucket_(token_bucket_capacity_) { 88 DCHECK_GT(capture_period_.InMicroseconds(), 0); 89 } 90 91 bool SmoothEventSampler::AddEventAndConsiderSampling( 92 base::TimeTicks event_time) { 93 DCHECK(!event_time.is_null()); 94 95 // Add tokens to the bucket based on advancement in time. Then, re-bound the 96 // number of tokens in the bucket. Overflow occurs when there is too much 97 // time between events (a common case), or when RecordSample() is not being 98 // called often enough (a bug). On the other hand, if RecordSample() is being 99 // called too often (e.g., as a reaction to IsOverdueForSamplingAt()), the 100 // bucket will underflow. 101 if (!current_event_.is_null()) { 102 if (current_event_ < event_time) { 103 token_bucket_ += event_time - current_event_; 104 if (token_bucket_ > token_bucket_capacity_) 105 token_bucket_ = token_bucket_capacity_; 106 } 107 // Side note: If the system clock is reset, causing |current_event_| to be 108 // greater than |event_time|, everything here will simply gracefully adjust. 109 if (token_bucket_ < base::TimeDelta()) 110 token_bucket_ = base::TimeDelta(); 111 TRACE_COUNTER1("mirroring", 112 "MirroringTokenBucketUsec", 113 std::max<int64>(0, token_bucket_.InMicroseconds())); 114 } 115 current_event_ = event_time; 116 117 // Return true if one capture period's worth of tokens are in the bucket. 118 return token_bucket_ >= capture_period_; 119 } 120 121 void SmoothEventSampler::RecordSample() { 122 token_bucket_ -= capture_period_; 123 TRACE_COUNTER1("mirroring", 124 "MirroringTokenBucketUsec", 125 std::max<int64>(0, token_bucket_.InMicroseconds())); 126 127 bool was_paused = overdue_sample_count_ == redundant_capture_goal_; 128 if (HasUnrecordedEvent()) { 129 last_sample_ = current_event_; 130 overdue_sample_count_ = 0; 131 } else { 132 ++overdue_sample_count_; 133 } 134 bool is_paused = overdue_sample_count_ == redundant_capture_goal_; 135 136 VLOG_IF(0, !was_paused && is_paused) 137 << "Tab content unchanged for " << redundant_capture_goal_ 138 << " frames; capture will halt until content changes."; 139 VLOG_IF(0, was_paused && !is_paused) 140 << "Content changed; capture will resume."; 141 } 142 143 bool SmoothEventSampler::IsOverdueForSamplingAt(base::TimeTicks event_time) 144 const { 145 DCHECK(!event_time.is_null()); 146 147 // If we don't get events on compositor updates on this platform, then we 148 // don't reliably know whether we're dirty. 149 if (events_are_reliable_) { 150 if (!HasUnrecordedEvent() && 151 overdue_sample_count_ >= redundant_capture_goal_) { 152 return false; // Not dirty. 153 } 154 } 155 156 if (last_sample_.is_null()) 157 return true; 158 159 // If we're dirty but not yet old, then we've recently gotten updates, so we 160 // won't request a sample just yet. 161 base::TimeDelta dirty_interval = event_time - last_sample_; 162 if (dirty_interval < capture_period_ * 4) 163 return false; 164 else 165 return true; 166 } 167 168 bool SmoothEventSampler::HasUnrecordedEvent() const { 169 return !current_event_.is_null() && current_event_ != last_sample_; 170 } 171 172 } // namespace content 173