modules/video_coding/codecs/vp8/screenshare_layers.cc - src.git - Git at Google

 /* Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */

 #include "modules/video_coding/codecs/vp8/screenshare_layers.h"

 #include <stdlib.h>

 #include <algorithm>
 #include <memory>

 #include "modules/video_coding/include/video_codec_interface.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
 #include "system_wrappers/include/clock.h"
 #include "system_wrappers/include/metrics.h"

 namespace webrtc {

 static const int kOneSecond90Khz = 90000;
 static const int kMinTimeBetweenSyncs = kOneSecond90Khz * 2;
 static const int kMaxTimeBetweenSyncs = kOneSecond90Khz * 4;
 static const int kQpDeltaThresholdForSync = 8;
 static const int kMinBitrateKbpsForQpBoost = 500;

 const double ScreenshareLayers::kMaxTL0FpsReduction = 2.5;
 const double ScreenshareLayers::kAcceptableTargetOvershoot = 2.0;

 constexpr int ScreenshareLayers::kMaxNumTemporalLayers;

 // Always emit a frame with certain interval, even if bitrate targets have
 // been exceeded. This prevents needless keyframe requests.
 const int ScreenshareLayers::kMaxFrameIntervalMs = 2750;

 ScreenshareLayers::ScreenshareLayers(int num_temporal_layers,
                                      Clock* clock)
     : clock_(clock),
       number_of_temporal_layers_(
           std::min(kMaxNumTemporalLayers, num_temporal_layers)),
       last_base_layer_sync_(false),
       active_layer_(-1),
       last_timestamp_(-1),
       last_sync_timestamp_(-1),
       last_emitted_tl0_timestamp_(-1),
       last_frame_time_ms_(-1),
       min_qp_(-1),
       max_qp_(-1),
       max_debt_bytes_(0),
       encode_framerate_(1000.0f, 1000.0f),  // 1 second window, second scale.
       bitrate_updated_(false) {
   RTC_CHECK_GT(number_of_temporal_layers_, 0);
   RTC_CHECK_LE(number_of_temporal_layers_, kMaxNumTemporalLayers);
 }

 ScreenshareLayers::~ScreenshareLayers() {
   UpdateHistograms();
 }

 TemporalLayers::FrameConfig ScreenshareLayers::UpdateLayerConfig(
     uint32_t timestamp) {
   if (number_of_temporal_layers_ <= 1) {
     // No flags needed for 1 layer screenshare.
     // TODO(pbos): Consider updating only last, and not all buffers.
     TemporalLayers::FrameConfig tl_config(
         kReferenceAndUpdate, kReferenceAndUpdate, kReferenceAndUpdate);
     return tl_config;
   }

   const int64_t now_ms = clock_->TimeInMilliseconds();

   int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
   int64_t ts_diff;
   if (last_timestamp_ == -1) {
     ts_diff = kOneSecond90Khz / capture_framerate_.value_or(*target_framerate_);
   } else {
     ts_diff = unwrapped_timestamp - last_timestamp_;
   }

   if (target_framerate_) {
     // If input frame rate exceeds target frame rate, either over a one second
     // averaging window, or if frame interval is below 90% of desired value,
     // drop frame.
     if (encode_framerate_.Rate(now_ms).value_or(0) > *target_framerate_)
       return TemporalLayers::FrameConfig(kNone, kNone, kNone);

     // Primarily check if frame interval is too short using frame timestamps,
     // as if they are correct they won't be affected by queuing in webrtc.
     const int64_t expected_frame_interval_90khz =
         kOneSecond90Khz / *target_framerate_;
     if (last_timestamp_ != -1 && ts_diff > 0) {
       if (ts_diff < 85 * expected_frame_interval_90khz / 100) {
         return TemporalLayers::FrameConfig(kNone, kNone, kNone);
       }
     } else {
       // Timestamps looks off, use realtime clock here instead.
       const int64_t expected_frame_interval_ms = 1000 / *target_framerate_;
       if (last_frame_time_ms_ != -1 &&
           now_ms - last_frame_time_ms_ <
               (85 * expected_frame_interval_ms) / 100) {
         return TemporalLayers::FrameConfig(kNone, kNone, kNone);
       }
     }
   }

   if (stats_.first_frame_time_ms_ == -1)
     stats_.first_frame_time_ms_ = now_ms;

   // Make sure both frame droppers leak out bits.
   layers_[0].UpdateDebt(ts_diff / 90);
   layers_[1].UpdateDebt(ts_diff / 90);
   last_timestamp_ = timestamp;
   last_frame_time_ms_ = now_ms;

   TemporalLayerState layer_state = TemporalLayerState::kDrop;

   if (active_layer_ == -1 ||
       layers_[active_layer_].state != TemporalLayer::State::kDropped) {
     if (last_emitted_tl0_timestamp_ != -1 &&
         (unwrapped_timestamp - last_emitted_tl0_timestamp_) / 90 >
             kMaxFrameIntervalMs) {
       // Too long time has passed since the last frame was emitted, cancel
       // enough debt to allow a single frame.
       layers_[0].debt_bytes_ = max_debt_bytes_ - 1;
     }
     if (layers_[0].debt_bytes_ > max_debt_bytes_) {
       // Must drop TL0, encode TL1 instead.
       if (layers_[1].debt_bytes_ > max_debt_bytes_) {
         // Must drop both TL0 and TL1.
         active_layer_ = -1;
       } else {
         active_layer_ = 1;
       }
     } else {
       active_layer_ = 0;
     }
   }

   switch (active_layer_) {
     case 0:
       layer_state = TemporalLayerState::kTl0;
       last_emitted_tl0_timestamp_ = unwrapped_timestamp;
       break;
     case 1:
       if (layers_[1].state != TemporalLayer::State::kDropped) {
         if (TimeToSync(unwrapped_timestamp)) {
           last_sync_timestamp_ = unwrapped_timestamp;
           layer_state = TemporalLayerState::kTl1Sync;
         } else {
           layer_state = TemporalLayerState::kTl1;
         }
       } else {
         layer_state = last_sync_timestamp_ == unwrapped_timestamp
                           ? TemporalLayerState::kTl1Sync
                           : TemporalLayerState::kTl1;
       }
       break;
     case -1:
       layer_state = TemporalLayerState::kDrop;
       ++stats_.num_dropped_frames_;
       break;
     default:
       RTC_NOTREACHED();
   }

   TemporalLayers::FrameConfig tl_config;
   // TODO(pbos): Consider referencing but not updating the 'alt' buffer for all
   // layers.
   switch (layer_state) {
     case TemporalLayerState::kDrop:
       tl_config = TemporalLayers::FrameConfig(kNone, kNone, kNone);
       break;
     case TemporalLayerState::kTl0:
       // TL0 only references and updates 'last'.
       tl_config =
           TemporalLayers::FrameConfig(kReferenceAndUpdate, kNone, kNone);
       tl_config.packetizer_temporal_idx = 0;
       break;
     case TemporalLayerState::kTl1:
       // TL1 references both 'last' and 'golden' but only updates 'golden'.
       tl_config =
           TemporalLayers::FrameConfig(kReference, kReferenceAndUpdate, kNone);
       tl_config.packetizer_temporal_idx = 1;
       break;
     case TemporalLayerState::kTl1Sync:
       // Predict from only TL0 to allow participants to switch to the high
       // bitrate stream. Updates 'golden' so that TL1 can continue to refer to
       // and update 'golden' from this point on.
       tl_config = TemporalLayers::FrameConfig(kReference, kUpdate, kNone);
       tl_config.packetizer_temporal_idx = 1;
       break;
   }

   tl_config.layer_sync = layer_state == TemporalLayerState::kTl1Sync;
   return tl_config;
 }

 void ScreenshareLayers::OnRatesUpdated(
     const std::vector<uint32_t>& bitrates_bps,
     int framerate_fps) {
   RTC_DCHECK_GT(framerate_fps, 0);
   RTC_DCHECK_GE(bitrates_bps.size(), 1);
   RTC_DCHECK_LE(bitrates_bps.size(), 2);

   // |bitrates_bps| uses individual rates per layer, but we want to use the
   // accumulated rate here.
   uint32_t tl0_kbps = bitrates_bps[0] / 1000;
   uint32_t tl1_kbps = tl0_kbps;
   if (bitrates_bps.size() > 1) {
     tl1_kbps += bitrates_bps[1] / 1000;
   }

   if (!target_framerate_) {
     // First OnRatesUpdated() is called during construction, with the
     // configured targets as parameters.
     target_framerate_ = framerate_fps;
     capture_framerate_ = target_framerate_;
     bitrate_updated_ = true;
   } else {
     if ((capture_framerate_ &&
          framerate_fps != static_cast<int>(*capture_framerate_)) ||
         (tl0_kbps != layers_[0].target_rate_kbps_) ||
         (tl1_kbps != layers_[1].target_rate_kbps_)) {
       bitrate_updated_ = true;
     }

     if (framerate_fps < 0) {
       capture_framerate_.reset();
     } else {
       capture_framerate_ = framerate_fps;
     }
   }

   layers_[0].target_rate_kbps_ = tl0_kbps;
   layers_[1].target_rate_kbps_ = tl1_kbps;
 }

 void ScreenshareLayers::FrameEncoded(unsigned int size, int qp) {
   if (size > 0)
     encode_framerate_.Update(1, clock_->TimeInMilliseconds());

   if (number_of_temporal_layers_ == 1)
     return;

   RTC_DCHECK_NE(-1, active_layer_);
   if (size == 0) {
     layers_[active_layer_].state = TemporalLayer::State::kDropped;
     ++stats_.num_overshoots_;
     return;
   }

   if (layers_[active_layer_].state == TemporalLayer::State::kDropped) {
     layers_[active_layer_].state = TemporalLayer::State::kQualityBoost;
   }

   if (qp != -1)
     layers_[active_layer_].last_qp = qp;

   if (active_layer_ == 0) {
     layers_[0].debt_bytes_ += size;
     layers_[1].debt_bytes_ += size;
     ++stats_.num_tl0_frames_;
     stats_.tl0_target_bitrate_sum_ += layers_[0].target_rate_kbps_;
     stats_.tl0_qp_sum_ += qp;
   } else if (active_layer_ == 1) {
     layers_[1].debt_bytes_ += size;
     ++stats_.num_tl1_frames_;
     stats_.tl1_target_bitrate_sum_ += layers_[1].target_rate_kbps_;
     stats_.tl1_qp_sum_ += qp;
   }
 }

 void ScreenshareLayers::PopulateCodecSpecific(
     bool frame_is_keyframe,
     const TemporalLayers::FrameConfig& tl_config,
     CodecSpecificInfoVP8* vp8_info,
     uint32_t timestamp) {
   if (number_of_temporal_layers_ == 1) {
     vp8_info->temporalIdx = kNoTemporalIdx;
     vp8_info->layerSync = false;
   } else {
     int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
     vp8_info->temporalIdx = tl_config.packetizer_temporal_idx;
     vp8_info->layerSync = tl_config.layer_sync;
     if (frame_is_keyframe) {
       vp8_info->temporalIdx = 0;
       last_sync_timestamp_ = unwrapped_timestamp;
       vp8_info->layerSync = true;
     } else if (last_base_layer_sync_ && vp8_info->temporalIdx != 0) {
       // Regardless of pattern the frame after a base layer sync will always
       // be a layer sync.
       last_sync_timestamp_ = unwrapped_timestamp;
       vp8_info->layerSync = true;
     }
     last_base_layer_sync_ = frame_is_keyframe;
   }
 }

 bool ScreenshareLayers::TimeToSync(int64_t timestamp) const {
   RTC_DCHECK_EQ(1, active_layer_);
   RTC_DCHECK_NE(-1, layers_[0].last_qp);
   if (layers_[1].last_qp == -1) {
     // First frame in TL1 should only depend on TL0 since there are no
     // previous frames in TL1.
     return true;
   }

   RTC_DCHECK_NE(-1, last_sync_timestamp_);
   int64_t timestamp_diff = timestamp - last_sync_timestamp_;
   if (timestamp_diff > kMaxTimeBetweenSyncs) {
     // After a certain time, force a sync frame.
     return true;
   } else if (timestamp_diff < kMinTimeBetweenSyncs) {
     // If too soon from previous sync frame, don't issue a new one.
     return false;
   }
   // Issue a sync frame if difference in quality between TL0 and TL1 isn't too
   // large.
   if (layers_[0].last_qp - layers_[1].last_qp < kQpDeltaThresholdForSync)
     return true;
   return false;
 }

 uint32_t ScreenshareLayers::GetCodecTargetBitrateKbps() const {
   uint32_t target_bitrate_kbps = layers_[0].target_rate_kbps_;

   if (number_of_temporal_layers_ > 1) {
     // Calculate a codec target bitrate. This may be higher than TL0, gaining
     // quality at the expense of frame rate at TL0. Constraints:
     // - TL0 frame rate no less than framerate / kMaxTL0FpsReduction.
     // - Target rate * kAcceptableTargetOvershoot should not exceed TL1 rate.
     target_bitrate_kbps =
         std::min(layers_[0].target_rate_kbps_ * kMaxTL0FpsReduction,
                  layers_[1].target_rate_kbps_ / kAcceptableTargetOvershoot);
   }

   return std::max(layers_[0].target_rate_kbps_, target_bitrate_kbps);
 }

 bool ScreenshareLayers::UpdateConfiguration(Vp8EncoderConfig* cfg) {
   bool cfg_updated = false;
   uint32_t target_bitrate_kbps = GetCodecTargetBitrateKbps();

   // TODO(sprang): We _really_ need to make an overhaul of this class. :(
   // If we're dropping frames in order to meet a target framerate, adjust the
   // bitrate assigned to the encoder so the total average bitrate is correct.
   float encoder_config_bitrate_kbps = target_bitrate_kbps;
   if (target_framerate_ && capture_framerate_ &&
       *target_framerate_ < *capture_framerate_) {
     encoder_config_bitrate_kbps *=
         static_cast<float>(*capture_framerate_) / *target_framerate_;
   }

   if (bitrate_updated_ ||
       cfg->rc_target_bitrate != encoder_config_bitrate_kbps) {
     cfg->rc_target_bitrate = encoder_config_bitrate_kbps;

     // Don't reconfigure qp limits during quality boost frames.
     if (active_layer_ == -1 ||
         layers_[active_layer_].state != TemporalLayer::State::kQualityBoost) {
       min_qp_ = cfg->rc_min_quantizer;
       max_qp_ = cfg->rc_max_quantizer;
       // After a dropped frame, a frame with max qp will be encoded and the
       // quality will then ramp up from there. To boost the speed of recovery,
       // encode the next frame with lower max qp, if there is sufficient
       // bandwidth to do so without causing excessive delay.
       // TL0 is the most important to improve since the errors in this layer
       // will propagate to TL1.
       // Currently, reduce max qp by 20% for TL0 and 15% for TL1.
       if (layers_[1].target_rate_kbps_ >= kMinBitrateKbpsForQpBoost) {
         layers_[0].enhanced_max_qp =
             min_qp_ + (((max_qp_ - min_qp_) * 80) / 100);
         layers_[1].enhanced_max_qp =
             min_qp_ + (((max_qp_ - min_qp_) * 85) / 100);
       } else {
         layers_[0].enhanced_max_qp = -1;
         layers_[1].enhanced_max_qp = -1;
       }
     }

     if (capture_framerate_) {
       int avg_frame_size =
           (target_bitrate_kbps * 1000) / (8 * *capture_framerate_);
       // Allow max debt to be the size of a single optimal frame.
       // TODO(sprang): Determine if this needs to be adjusted by some factor.
       // (Lower values may cause more frame drops, higher may lead to queuing
       // delays.)
       max_debt_bytes_ = avg_frame_size;
     }

     bitrate_updated_ = false;
     cfg_updated = true;
   }

   // Don't try to update boosts state if not active yet.
   if (active_layer_ == -1)
     return cfg_updated;

   if (max_qp_ == -1 || number_of_temporal_layers_ <= 1)
     return cfg_updated;

   // If layer is in the quality boost state (following a dropped frame), update
   // the configuration with the adjusted (lower) qp and set the state back to
   // normal.
   unsigned int adjusted_max_qp;
   if (layers_[active_layer_].state == TemporalLayer::State::kQualityBoost &&
       layers_[active_layer_].enhanced_max_qp != -1) {
     adjusted_max_qp = layers_[active_layer_].enhanced_max_qp;
     layers_[active_layer_].state = TemporalLayer::State::kNormal;
   } else {
     adjusted_max_qp = max_qp_;  // Set the normal max qp.
   }

   if (adjusted_max_qp == cfg->rc_max_quantizer)
     return cfg_updated;

   cfg->rc_max_quantizer = adjusted_max_qp;
   cfg_updated = true;

   return cfg_updated;
 }

 void ScreenshareLayers::TemporalLayer::UpdateDebt(int64_t delta_ms) {
   uint32_t debt_reduction_bytes = target_rate_kbps_ * delta_ms / 8;
   if (debt_reduction_bytes >= debt_bytes_) {
     debt_bytes_ = 0;
   } else {
     debt_bytes_ -= debt_reduction_bytes;
   }
 }

 void ScreenshareLayers::UpdateHistograms() {
   if (stats_.first_frame_time_ms_ == -1)
     return;
   int64_t duration_sec =
       (clock_->TimeInMilliseconds() - stats_.first_frame_time_ms_ + 500) / 1000;
   if (duration_sec >= metrics::kMinRunTimeInSeconds) {
     RTC_HISTOGRAM_COUNTS_10000(
         "WebRTC.Video.Screenshare.Layer0.FrameRate",
         (stats_.num_tl0_frames_ + (duration_sec / 2)) / duration_sec);
     RTC_HISTOGRAM_COUNTS_10000(
         "WebRTC.Video.Screenshare.Layer1.FrameRate",
         (stats_.num_tl1_frames_ + (duration_sec / 2)) / duration_sec);
     int total_frames = stats_.num_tl0_frames_ + stats_.num_tl1_frames_;
     RTC_HISTOGRAM_COUNTS_10000(
         "WebRTC.Video.Screenshare.FramesPerDrop",
         (stats_.num_dropped_frames_ == 0
              ? 0
              : total_frames / stats_.num_dropped_frames_));
     RTC_HISTOGRAM_COUNTS_10000(
         "WebRTC.Video.Screenshare.FramesPerOvershoot",
         (stats_.num_overshoots_ == 0 ? 0
                                      : total_frames / stats_.num_overshoots_));
     if (stats_.num_tl0_frames_ > 0) {
       RTC_HISTOGRAM_COUNTS_10000("WebRTC.Video.Screenshare.Layer0.Qp",
                                  stats_.tl0_qp_sum_ / stats_.num_tl0_frames_);
       RTC_HISTOGRAM_COUNTS_10000(
           "WebRTC.Video.Screenshare.Layer0.TargetBitrate",
           stats_.tl0_target_bitrate_sum_ / stats_.num_tl0_frames_);
     }
     if (stats_.num_tl1_frames_ > 0) {
       RTC_HISTOGRAM_COUNTS_10000("WebRTC.Video.Screenshare.Layer1.Qp",
                                  stats_.tl1_qp_sum_ / stats_.num_tl1_frames_);
       RTC_HISTOGRAM_COUNTS_10000(
           "WebRTC.Video.Screenshare.Layer1.TargetBitrate",
           stats_.tl1_target_bitrate_sum_ / stats_.num_tl1_frames_);
     }
   }
 }
 }  // namespace webrtc
	/* Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*/

	#include "modules/video_coding/codecs/vp8/screenshare_layers.h"

	#include <stdlib.h>

	#include <algorithm>
	#include <memory>

	#include "modules/video_coding/include/video_codec_interface.h"
	#include "rtc_base/checks.h"
	#include "rtc_base/logging.h"
	#include "system_wrappers/include/clock.h"
	#include "system_wrappers/include/metrics.h"

	namespace webrtc {

	static const int kOneSecond90Khz = 90000;
	static const int kMinTimeBetweenSyncs = kOneSecond90Khz * 2;
	static const int kMaxTimeBetweenSyncs = kOneSecond90Khz * 4;
	static const int kQpDeltaThresholdForSync = 8;
	static const int kMinBitrateKbpsForQpBoost = 500;

	const double ScreenshareLayers::kMaxTL0FpsReduction = 2.5;
	const double ScreenshareLayers::kAcceptableTargetOvershoot = 2.0;

	constexpr int ScreenshareLayers::kMaxNumTemporalLayers;

	// Always emit a frame with certain interval, even if bitrate targets have
	// been exceeded. This prevents needless keyframe requests.
	const int ScreenshareLayers::kMaxFrameIntervalMs = 2750;

	ScreenshareLayers::ScreenshareLayers(int num_temporal_layers,
	Clock* clock)
	: clock_(clock),
	number_of_temporal_layers_(
	std::min(kMaxNumTemporalLayers, num_temporal_layers)),
	last_base_layer_sync_(false),
	active_layer_(-1),
	last_timestamp_(-1),
	last_sync_timestamp_(-1),
	last_emitted_tl0_timestamp_(-1),
	last_frame_time_ms_(-1),
	min_qp_(-1),
	max_qp_(-1),
	max_debt_bytes_(0),
	encode_framerate_(1000.0f, 1000.0f), // 1 second window, second scale.
	bitrate_updated_(false) {
	RTC_CHECK_GT(number_of_temporal_layers_, 0);
	RTC_CHECK_LE(number_of_temporal_layers_, kMaxNumTemporalLayers);
	}

	ScreenshareLayers::~ScreenshareLayers() {
	UpdateHistograms();
	}

	TemporalLayers::FrameConfig ScreenshareLayers::UpdateLayerConfig(
	uint32_t timestamp) {
	if (number_of_temporal_layers_ <= 1) {
	// No flags needed for 1 layer screenshare.
	// TODO(pbos): Consider updating only last, and not all buffers.
	TemporalLayers::FrameConfig tl_config(
	kReferenceAndUpdate, kReferenceAndUpdate, kReferenceAndUpdate);
	return tl_config;
	}

	const int64_t now_ms = clock_->TimeInMilliseconds();

	int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
	int64_t ts_diff;
	if (last_timestamp_ == -1) {
	ts_diff = kOneSecond90Khz / capture_framerate_.value_or(*target_framerate_);
	} else {
	ts_diff = unwrapped_timestamp - last_timestamp_;
	}

	if (target_framerate_) {
	// If input frame rate exceeds target frame rate, either over a one second
	// averaging window, or if frame interval is below 90% of desired value,
	// drop frame.
	if (encode_framerate_.Rate(now_ms).value_or(0) > *target_framerate_)
	return TemporalLayers::FrameConfig(kNone, kNone, kNone);

	// Primarily check if frame interval is too short using frame timestamps,
	// as if they are correct they won't be affected by queuing in webrtc.
	const int64_t expected_frame_interval_90khz =
	kOneSecond90Khz / *target_framerate_;
	if (last_timestamp_ != -1 && ts_diff > 0) {
	if (ts_diff < 85 * expected_frame_interval_90khz / 100) {
	return TemporalLayers::FrameConfig(kNone, kNone, kNone);
	}
	} else {
	// Timestamps looks off, use realtime clock here instead.
	const int64_t expected_frame_interval_ms = 1000 / *target_framerate_;
	if (last_frame_time_ms_ != -1 &&
	now_ms - last_frame_time_ms_ <
	(85 * expected_frame_interval_ms) / 100) {
	return TemporalLayers::FrameConfig(kNone, kNone, kNone);
	}
	}
	}

	if (stats_.first_frame_time_ms_ == -1)
	stats_.first_frame_time_ms_ = now_ms;

	// Make sure both frame droppers leak out bits.
	layers_[0].UpdateDebt(ts_diff / 90);
	layers_[1].UpdateDebt(ts_diff / 90);
	last_timestamp_ = timestamp;
	last_frame_time_ms_ = now_ms;

	TemporalLayerState layer_state = TemporalLayerState::kDrop;

	if (active_layer_ == -1 \|\|
	layers_[active_layer_].state != TemporalLayer::State::kDropped) {
	if (last_emitted_tl0_timestamp_ != -1 &&
	(unwrapped_timestamp - last_emitted_tl0_timestamp_) / 90 >
	kMaxFrameIntervalMs) {
	// Too long time has passed since the last frame was emitted, cancel
	// enough debt to allow a single frame.
	layers_[0].debt_bytes_ = max_debt_bytes_ - 1;
	}
	if (layers_[0].debt_bytes_ > max_debt_bytes_) {
	// Must drop TL0, encode TL1 instead.
	if (layers_[1].debt_bytes_ > max_debt_bytes_) {
	// Must drop both TL0 and TL1.
	active_layer_ = -1;
	} else {
	active_layer_ = 1;
	}
	} else {
	active_layer_ = 0;
	}
	}

	switch (active_layer_) {
	case 0:
	layer_state = TemporalLayerState::kTl0;
	last_emitted_tl0_timestamp_ = unwrapped_timestamp;
	break;
	case 1:
	if (layers_[1].state != TemporalLayer::State::kDropped) {
	if (TimeToSync(unwrapped_timestamp)) {
	last_sync_timestamp_ = unwrapped_timestamp;
	layer_state = TemporalLayerState::kTl1Sync;
	} else {
	layer_state = TemporalLayerState::kTl1;
	}
	} else {
	layer_state = last_sync_timestamp_ == unwrapped_timestamp
	? TemporalLayerState::kTl1Sync
	: TemporalLayerState::kTl1;
	}
	break;
	case -1:
	layer_state = TemporalLayerState::kDrop;
	++stats_.num_dropped_frames_;
	break;
	default:
	RTC_NOTREACHED();
	}

	TemporalLayers::FrameConfig tl_config;
	// TODO(pbos): Consider referencing but not updating the 'alt' buffer for all
	// layers.
	switch (layer_state) {
	case TemporalLayerState::kDrop:
	tl_config = TemporalLayers::FrameConfig(kNone, kNone, kNone);
	break;
	case TemporalLayerState::kTl0:
	// TL0 only references and updates 'last'.
	tl_config =
	TemporalLayers::FrameConfig(kReferenceAndUpdate, kNone, kNone);
	tl_config.packetizer_temporal_idx = 0;
	break;
	case TemporalLayerState::kTl1:
	// TL1 references both 'last' and 'golden' but only updates 'golden'.
	tl_config =
	TemporalLayers::FrameConfig(kReference, kReferenceAndUpdate, kNone);
	tl_config.packetizer_temporal_idx = 1;
	break;
	case TemporalLayerState::kTl1Sync:
	// Predict from only TL0 to allow participants to switch to the high
	// bitrate stream. Updates 'golden' so that TL1 can continue to refer to
	// and update 'golden' from this point on.
	tl_config = TemporalLayers::FrameConfig(kReference, kUpdate, kNone);
	tl_config.packetizer_temporal_idx = 1;
	break;
	}

	tl_config.layer_sync = layer_state == TemporalLayerState::kTl1Sync;
	return tl_config;
	}

	void ScreenshareLayers::OnRatesUpdated(
	const std::vector<uint32_t>& bitrates_bps,
	int framerate_fps) {
	RTC_DCHECK_GT(framerate_fps, 0);
	RTC_DCHECK_GE(bitrates_bps.size(), 1);
	RTC_DCHECK_LE(bitrates_bps.size(), 2);

	// \|bitrates_bps\| uses individual rates per layer, but we want to use the
	// accumulated rate here.
	uint32_t tl0_kbps = bitrates_bps[0] / 1000;
	uint32_t tl1_kbps = tl0_kbps;
	if (bitrates_bps.size() > 1) {
	tl1_kbps += bitrates_bps[1] / 1000;
	}

	if (!target_framerate_) {
	// First OnRatesUpdated() is called during construction, with the
	// configured targets as parameters.
	target_framerate_ = framerate_fps;
	capture_framerate_ = target_framerate_;
	bitrate_updated_ = true;
	} else {
	if ((capture_framerate_ &&
	framerate_fps != static_cast<int>(*capture_framerate_)) \|\|
	(tl0_kbps != layers_[0].target_rate_kbps_) \|\|
	(tl1_kbps != layers_[1].target_rate_kbps_)) {
	bitrate_updated_ = true;
	}

	if (framerate_fps < 0) {
	capture_framerate_.reset();
	} else {
	capture_framerate_ = framerate_fps;
	}
	}

	layers_[0].target_rate_kbps_ = tl0_kbps;
	layers_[1].target_rate_kbps_ = tl1_kbps;
	}

	void ScreenshareLayers::FrameEncoded(unsigned int size, int qp) {
	if (size > 0)
	encode_framerate_.Update(1, clock_->TimeInMilliseconds());

	if (number_of_temporal_layers_ == 1)
	return;

	RTC_DCHECK_NE(-1, active_layer_);
	if (size == 0) {
	layers_[active_layer_].state = TemporalLayer::State::kDropped;
	++stats_.num_overshoots_;
	return;
	}

	if (layers_[active_layer_].state == TemporalLayer::State::kDropped) {
	layers_[active_layer_].state = TemporalLayer::State::kQualityBoost;
	}

	if (qp != -1)
	layers_[active_layer_].last_qp = qp;

	if (active_layer_ == 0) {
	layers_[0].debt_bytes_ += size;
	layers_[1].debt_bytes_ += size;
	++stats_.num_tl0_frames_;
	stats_.tl0_target_bitrate_sum_ += layers_[0].target_rate_kbps_;
	stats_.tl0_qp_sum_ += qp;
	} else if (active_layer_ == 1) {
	layers_[1].debt_bytes_ += size;
	++stats_.num_tl1_frames_;
	stats_.tl1_target_bitrate_sum_ += layers_[1].target_rate_kbps_;
	stats_.tl1_qp_sum_ += qp;
	}
	}

	void ScreenshareLayers::PopulateCodecSpecific(
	bool frame_is_keyframe,
	const TemporalLayers::FrameConfig& tl_config,
	CodecSpecificInfoVP8* vp8_info,
	uint32_t timestamp) {
	if (number_of_temporal_layers_ == 1) {
	vp8_info->temporalIdx = kNoTemporalIdx;
	vp8_info->layerSync = false;
	} else {
	int64_t unwrapped_timestamp = time_wrap_handler_.Unwrap(timestamp);
	vp8_info->temporalIdx = tl_config.packetizer_temporal_idx;
	vp8_info->layerSync = tl_config.layer_sync;
	if (frame_is_keyframe) {
	vp8_info->temporalIdx = 0;
	last_sync_timestamp_ = unwrapped_timestamp;
	vp8_info->layerSync = true;
	} else if (last_base_layer_sync_ && vp8_info->temporalIdx != 0) {
	// Regardless of pattern the frame after a base layer sync will always
	// be a layer sync.
	last_sync_timestamp_ = unwrapped_timestamp;
	vp8_info->layerSync = true;
	}
	last_base_layer_sync_ = frame_is_keyframe;
	}
	}

	bool ScreenshareLayers::TimeToSync(int64_t timestamp) const {
	RTC_DCHECK_EQ(1, active_layer_);
	RTC_DCHECK_NE(-1, layers_[0].last_qp);
	if (layers_[1].last_qp == -1) {
	// First frame in TL1 should only depend on TL0 since there are no
	// previous frames in TL1.
	return true;
	}

	RTC_DCHECK_NE(-1, last_sync_timestamp_);
	int64_t timestamp_diff = timestamp - last_sync_timestamp_;
	if (timestamp_diff > kMaxTimeBetweenSyncs) {
	// After a certain time, force a sync frame.
	return true;
	} else if (timestamp_diff < kMinTimeBetweenSyncs) {
	// If too soon from previous sync frame, don't issue a new one.
	return false;
	}
	// Issue a sync frame if difference in quality between TL0 and TL1 isn't too
	// large.
	if (layers_[0].last_qp - layers_[1].last_qp < kQpDeltaThresholdForSync)
	return true;
	return false;
	}

	uint32_t ScreenshareLayers::GetCodecTargetBitrateKbps() const {
	uint32_t target_bitrate_kbps = layers_[0].target_rate_kbps_;

	if (number_of_temporal_layers_ > 1) {
	// Calculate a codec target bitrate. This may be higher than TL0, gaining
	// quality at the expense of frame rate at TL0. Constraints:
	// - TL0 frame rate no less than framerate / kMaxTL0FpsReduction.
	// - Target rate * kAcceptableTargetOvershoot should not exceed TL1 rate.
	target_bitrate_kbps =
	std::min(layers_[0].target_rate_kbps_ * kMaxTL0FpsReduction,
	layers_[1].target_rate_kbps_ / kAcceptableTargetOvershoot);
	}

	return std::max(layers_[0].target_rate_kbps_, target_bitrate_kbps);
	}

	bool ScreenshareLayers::UpdateConfiguration(Vp8EncoderConfig* cfg) {
	bool cfg_updated = false;
	uint32_t target_bitrate_kbps = GetCodecTargetBitrateKbps();

	// TODO(sprang): We _really_ need to make an overhaul of this class. :(
	// If we're dropping frames in order to meet a target framerate, adjust the
	// bitrate assigned to the encoder so the total average bitrate is correct.
	float encoder_config_bitrate_kbps = target_bitrate_kbps;
	if (target_framerate_ && capture_framerate_ &&
	target_framerate_ < capture_framerate_) {
	encoder_config_bitrate_kbps *=
	static_cast<float>(capture_framerate_) / target_framerate_;
	}

	if (bitrate_updated_ \|\|
	cfg->rc_target_bitrate != encoder_config_bitrate_kbps) {
	cfg->rc_target_bitrate = encoder_config_bitrate_kbps;

	// Don't reconfigure qp limits during quality boost frames.
	if (active_layer_ == -1 \|\|
	layers_[active_layer_].state != TemporalLayer::State::kQualityBoost) {
	min_qp_ = cfg->rc_min_quantizer;
	max_qp_ = cfg->rc_max_quantizer;
	// After a dropped frame, a frame with max qp will be encoded and the
	// quality will then ramp up from there. To boost the speed of recovery,
	// encode the next frame with lower max qp, if there is sufficient
	// bandwidth to do so without causing excessive delay.
	// TL0 is the most important to improve since the errors in this layer
	// will propagate to TL1.
	// Currently, reduce max qp by 20% for TL0 and 15% for TL1.
	if (layers_[1].target_rate_kbps_ >= kMinBitrateKbpsForQpBoost) {
	layers_[0].enhanced_max_qp =
	min_qp_ + (((max_qp_ - min_qp_) * 80) / 100);
	layers_[1].enhanced_max_qp =
	min_qp_ + (((max_qp_ - min_qp_) * 85) / 100);
	} else {
	layers_[0].enhanced_max_qp = -1;
	layers_[1].enhanced_max_qp = -1;
	}
	}

	if (capture_framerate_) {
	int avg_frame_size =
	(target_bitrate_kbps * 1000) / (8 * *capture_framerate_);
	// Allow max debt to be the size of a single optimal frame.
	// TODO(sprang): Determine if this needs to be adjusted by some factor.
	// (Lower values may cause more frame drops, higher may lead to queuing
	// delays.)
	max_debt_bytes_ = avg_frame_size;
	}

	bitrate_updated_ = false;
	cfg_updated = true;
	}

	// Don't try to update boosts state if not active yet.
	if (active_layer_ == -1)
	return cfg_updated;

	if (max_qp_ == -1 \|\| number_of_temporal_layers_ <= 1)
	return cfg_updated;

	// If layer is in the quality boost state (following a dropped frame), update
	// the configuration with the adjusted (lower) qp and set the state back to
	// normal.
	unsigned int adjusted_max_qp;
	if (layers_[active_layer_].state == TemporalLayer::State::kQualityBoost &&
	layers_[active_layer_].enhanced_max_qp != -1) {
	adjusted_max_qp = layers_[active_layer_].enhanced_max_qp;
	layers_[active_layer_].state = TemporalLayer::State::kNormal;
	} else {
	adjusted_max_qp = max_qp_; // Set the normal max qp.
	}

	if (adjusted_max_qp == cfg->rc_max_quantizer)
	return cfg_updated;

	cfg->rc_max_quantizer = adjusted_max_qp;
	cfg_updated = true;

	return cfg_updated;
	}

	void ScreenshareLayers::TemporalLayer::UpdateDebt(int64_t delta_ms) {
	uint32_t debt_reduction_bytes = target_rate_kbps_ * delta_ms / 8;
	if (debt_reduction_bytes >= debt_bytes_) {
	debt_bytes_ = 0;
	} else {
	debt_bytes_ -= debt_reduction_bytes;
	}
	}

	void ScreenshareLayers::UpdateHistograms() {
	if (stats_.first_frame_time_ms_ == -1)
	return;
	int64_t duration_sec =
	(clock_->TimeInMilliseconds() - stats_.first_frame_time_ms_ + 500) / 1000;
	if (duration_sec >= metrics::kMinRunTimeInSeconds) {
	RTC_HISTOGRAM_COUNTS_10000(
	"WebRTC.Video.Screenshare.Layer0.FrameRate",
	(stats_.num_tl0_frames_ + (duration_sec / 2)) / duration_sec);
	RTC_HISTOGRAM_COUNTS_10000(
	"WebRTC.Video.Screenshare.Layer1.FrameRate",
	(stats_.num_tl1_frames_ + (duration_sec / 2)) / duration_sec);
	int total_frames = stats_.num_tl0_frames_ + stats_.num_tl1_frames_;
	RTC_HISTOGRAM_COUNTS_10000(
	"WebRTC.Video.Screenshare.FramesPerDrop",
	(stats_.num_dropped_frames_ == 0
	? 0
	: total_frames / stats_.num_dropped_frames_));
	RTC_HISTOGRAM_COUNTS_10000(
	"WebRTC.Video.Screenshare.FramesPerOvershoot",
	(stats_.num_overshoots_ == 0 ? 0
	: total_frames / stats_.num_overshoots_));
	if (stats_.num_tl0_frames_ > 0) {
	RTC_HISTOGRAM_COUNTS_10000("WebRTC.Video.Screenshare.Layer0.Qp",
	stats_.tl0_qp_sum_ / stats_.num_tl0_frames_);
	RTC_HISTOGRAM_COUNTS_10000(
	"WebRTC.Video.Screenshare.Layer0.TargetBitrate",
	stats_.tl0_target_bitrate_sum_ / stats_.num_tl0_frames_);
	}
	if (stats_.num_tl1_frames_ > 0) {
	RTC_HISTOGRAM_COUNTS_10000("WebRTC.Video.Screenshare.Layer1.Qp",
	stats_.tl1_qp_sum_ / stats_.num_tl1_frames_);
	RTC_HISTOGRAM_COUNTS_10000(
	"WebRTC.Video.Screenshare.Layer1.TargetBitrate",
	stats_.tl1_target_bitrate_sum_ / stats_.num_tl1_frames_);
	}
	}
	}
	} // namespace webrtc