modules/video_coding/utility/simulcast_rate_allocator.cc - src - Git at Google

 /*
  *  Copyright (c) 2016 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/utility/simulcast_rate_allocator.h"

 #include <stdio.h>

 #include <algorithm>
 #include <cmath>
 #include <cstdint>
 #include <numeric>
 #include <string>
 #include <tuple>
 #include <vector>

 #include "rtc_base/checks.h"
 #include "rtc_base/experiments/rate_control_settings.h"
 #include "system_wrappers/include/field_trial.h"

 namespace webrtc {
 namespace {
 // Ratio allocation between temporal streams:
 // Values as required for the VP8 codec (accumulating).
 static const float
     kLayerRateAllocation[kMaxTemporalStreams][kMaxTemporalStreams] = {
         {1.0f, 1.0f, 1.0f, 1.0f},  // 1 layer
         {0.6f, 1.0f, 1.0f, 1.0f},  // 2 layers {60%, 40%}
         {0.4f, 0.6f, 1.0f, 1.0f},  // 3 layers {40%, 20%, 40%}
         {0.25f, 0.4f, 0.6f, 1.0f}  // 4 layers {25%, 15%, 20%, 40%}
 };

 static const float kBaseHeavy3TlRateAllocation[kMaxTemporalStreams] = {
     0.6f, 0.8f, 1.0f, 1.0f  // 3 layers {60%, 20%, 20%}
 };

 const uint32_t kLegacyScreenshareTl0BitrateKbps = 200;
 const uint32_t kLegacyScreenshareTl1BitrateKbps = 1000;
 }  // namespace

 float SimulcastRateAllocator::GetTemporalRateAllocation(
     int num_layers,
     int temporal_id,
     bool base_heavy_tl3_alloc) {
   RTC_CHECK_GT(num_layers, 0);
   RTC_CHECK_LE(num_layers, kMaxTemporalStreams);
   RTC_CHECK_GE(temporal_id, 0);
   RTC_CHECK_LT(temporal_id, num_layers);
   if (num_layers == 3 && base_heavy_tl3_alloc) {
     return kBaseHeavy3TlRateAllocation[temporal_id];
   }
   return kLayerRateAllocation[num_layers - 1][temporal_id];
 }

 SimulcastRateAllocator::SimulcastRateAllocator(const VideoCodec& codec)
     : codec_(codec),
       stable_rate_settings_(StableTargetRateExperiment::ParseFromFieldTrials()),
       rate_control_settings_(RateControlSettings::ParseFromFieldTrials()) {}

 SimulcastRateAllocator::~SimulcastRateAllocator() = default;

 VideoBitrateAllocation SimulcastRateAllocator::Allocate(
     VideoBitrateAllocationParameters parameters) {
   VideoBitrateAllocation allocated_bitrates;
   DataRate stable_rate = parameters.total_bitrate;
   if (stable_rate_settings_.IsEnabled() &&
       parameters.stable_bitrate > DataRate::Zero()) {
     stable_rate = std::min(parameters.stable_bitrate, parameters.total_bitrate);
   }
   DistributeAllocationToSimulcastLayers(parameters.total_bitrate, stable_rate,
                                         &allocated_bitrates);
   DistributeAllocationToTemporalLayers(&allocated_bitrates);
   return allocated_bitrates;
 }

 void SimulcastRateAllocator::DistributeAllocationToSimulcastLayers(
     DataRate total_bitrate,
     DataRate stable_bitrate,
     VideoBitrateAllocation* allocated_bitrates) {
   DataRate left_in_total_allocation = total_bitrate;
   DataRate left_in_stable_allocation = stable_bitrate;

   if (codec_.maxBitrate) {
     DataRate max_rate = DataRate::kbps(codec_.maxBitrate);
     left_in_total_allocation = std::min(left_in_total_allocation, max_rate);
     left_in_stable_allocation = std::min(left_in_stable_allocation, max_rate);
   }

   if (codec_.numberOfSimulcastStreams == 0) {
     // No simulcast, just set the target as this has been capped already.
     if (codec_.active) {
       allocated_bitrates->SetBitrate(
           0, 0,
           std::max(DataRate::kbps(codec_.minBitrate), left_in_total_allocation)
               .bps());
     }
     return;
   }

   // Sort the layers by maxFramerate, they might not always be from smallest
   // to biggest
   std::vector<size_t> layer_index(codec_.numberOfSimulcastStreams);
   std::iota(layer_index.begin(), layer_index.end(), 0);
   std::stable_sort(layer_index.begin(), layer_index.end(),
                    [this](size_t a, size_t b) {
                      return std::tie(codec_.simulcastStream[a].maxBitrate) <
                             std::tie(codec_.simulcastStream[b].maxBitrate);
                    });

   // Find the first active layer. We don't allocate to inactive layers.
   size_t active_layer = 0;
   for (; active_layer < codec_.numberOfSimulcastStreams; ++active_layer) {
     if (codec_.simulcastStream[layer_index[active_layer]].active) {
       // Found the first active layer.
       break;
     }
   }
   // All streams could be inactive, and nothing more to do.
   if (active_layer == codec_.numberOfSimulcastStreams) {
     return;
   }

   // Always allocate enough bitrate for the minimum bitrate of the first
   // active layer. Suspending below min bitrate is controlled outside the
   // codec implementation and is not overridden by this.
   DataRate min_rate = DataRate::kbps(
       codec_.simulcastStream[layer_index[active_layer]].minBitrate);
   left_in_total_allocation = std::max(left_in_total_allocation, min_rate);
   left_in_stable_allocation = std::max(left_in_stable_allocation, min_rate);

   // Begin by allocating bitrate to simulcast streams, putting all bitrate in
   // temporal layer 0. We'll then distribute this bitrate, across potential
   // temporal layers, when stream allocation is done.

   bool first_allocation = false;
   if (stream_enabled_.empty()) {
     // First time allocating, this means we should not include hysteresis in
     // case this is a reconfiguration of an existing enabled stream.
     first_allocation = true;
     stream_enabled_.resize(codec_.numberOfSimulcastStreams, false);
   }

   size_t top_active_layer = active_layer;
   // Allocate up to the target bitrate for each active simulcast layer.
   for (; active_layer < codec_.numberOfSimulcastStreams; ++active_layer) {
     const SimulcastStream& stream =
         codec_.simulcastStream[layer_index[active_layer]];
     if (!stream.active) {
       stream_enabled_[layer_index[active_layer]] = false;
       continue;
     }
     // If we can't allocate to the current layer we can't allocate to higher
     // layers because they require a higher minimum bitrate.
     DataRate min_bitrate = DataRate::kbps(stream.minBitrate);
     DataRate target_bitrate = DataRate::kbps(stream.targetBitrate);
     double hysteresis_factor =
         codec_.mode == VideoCodecMode::kRealtimeVideo
             ? stable_rate_settings_.GetVideoHysteresisFactor()
             : stable_rate_settings_.GetScreenshareHysteresisFactor();
     if (!first_allocation && !stream_enabled_[layer_index[active_layer]]) {
       min_bitrate = std::min(hysteresis_factor * min_bitrate, target_bitrate);
     }
     if (left_in_stable_allocation < min_bitrate) {
       allocated_bitrates->set_bw_limited(true);
       break;
     }

     // We are allocating to this layer so it is the current active allocation.
     top_active_layer = layer_index[active_layer];
     stream_enabled_[layer_index[active_layer]] = true;
     DataRate layer_rate = std::min(left_in_total_allocation, target_bitrate);
     allocated_bitrates->SetBitrate(layer_index[active_layer], 0,
                                    layer_rate.bps());
     left_in_total_allocation -= layer_rate;
     left_in_stable_allocation -=
         std::min(left_in_stable_allocation, target_bitrate);
   }

   // All layers above this one are not active.
   for (; active_layer < codec_.numberOfSimulcastStreams; ++active_layer) {
     stream_enabled_[layer_index[active_layer]] = false;
   }

   // Next, try allocate remaining bitrate, up to max bitrate, in top active
   // stream.
   // TODO(sprang): Allocate up to max bitrate for all layers once we have a
   //               better idea of possible performance implications.
   if (left_in_total_allocation > DataRate::Zero()) {
     const SimulcastStream& stream = codec_.simulcastStream[top_active_layer];
     DataRate initial_layer_rate =
         DataRate::bps(allocated_bitrates->GetSpatialLayerSum(top_active_layer));
     DataRate additional_allocation =
         std::min(left_in_total_allocation,
                  DataRate::kbps(stream.maxBitrate) - initial_layer_rate);
     allocated_bitrates->SetBitrate(
         top_active_layer, 0,
         (initial_layer_rate + additional_allocation).bps());
   }
 }

 void SimulcastRateAllocator::DistributeAllocationToTemporalLayers(
     VideoBitrateAllocation* allocated_bitrates_bps) const {
   const int num_spatial_streams =
       std::max(1, static_cast<int>(codec_.numberOfSimulcastStreams));

   // Finally, distribute the bitrate for the simulcast streams across the
   // available temporal layers.
   for (int simulcast_id = 0; simulcast_id < num_spatial_streams;
        ++simulcast_id) {
     uint32_t target_bitrate_kbps =
         allocated_bitrates_bps->GetBitrate(simulcast_id, 0) / 1000;
     if (target_bitrate_kbps == 0) {
       continue;
     }

     const uint32_t expected_allocated_bitrate_kbps = target_bitrate_kbps;
     RTC_DCHECK_EQ(
         target_bitrate_kbps,
         allocated_bitrates_bps->GetSpatialLayerSum(simulcast_id) / 1000);
     const int num_temporal_streams = NumTemporalStreams(simulcast_id);
     uint32_t max_bitrate_kbps;
     // Legacy temporal-layered only screenshare, or simulcast screenshare
     // with legacy mode for simulcast stream 0.
     const bool conference_screenshare_mode =
         codec_.mode == VideoCodecMode::kScreensharing &&
         ((num_spatial_streams == 1 && num_temporal_streams == 2) ||  // Legacy.
          (num_spatial_streams > 1 && simulcast_id == 0 &&
           num_temporal_streams == 2));  // Simulcast.
     if (conference_screenshare_mode) {
       // TODO(holmer): This is a "temporary" hack for screensharing, where we
       // interpret the startBitrate as the encoder target bitrate. This is
       // to allow for a different max bitrate, so if the codec can't meet
       // the target we still allow it to overshoot up to the max before dropping
       // frames. This hack should be improved.
       max_bitrate_kbps =
           std::min(kLegacyScreenshareTl1BitrateKbps, target_bitrate_kbps);
       target_bitrate_kbps =
           std::min(kLegacyScreenshareTl0BitrateKbps, target_bitrate_kbps);
     } else if (num_spatial_streams == 1) {
       max_bitrate_kbps = codec_.maxBitrate;
     } else {
       max_bitrate_kbps = codec_.simulcastStream[simulcast_id].maxBitrate;
     }

     std::vector<uint32_t> tl_allocation;
     if (num_temporal_streams == 1) {
       tl_allocation.push_back(target_bitrate_kbps);
     } else {
       if (conference_screenshare_mode) {
         tl_allocation = ScreenshareTemporalLayerAllocation(
             target_bitrate_kbps, max_bitrate_kbps, simulcast_id);
       } else {
         tl_allocation = DefaultTemporalLayerAllocation(
             target_bitrate_kbps, max_bitrate_kbps, simulcast_id);
       }
     }
     RTC_DCHECK_GT(tl_allocation.size(), 0);
     RTC_DCHECK_LE(tl_allocation.size(), num_temporal_streams);

     uint64_t tl_allocation_sum_kbps = 0;
     for (size_t tl_index = 0; tl_index < tl_allocation.size(); ++tl_index) {
       uint32_t layer_rate_kbps = tl_allocation[tl_index];
       if (layer_rate_kbps > 0) {
         allocated_bitrates_bps->SetBitrate(simulcast_id, tl_index,
                                            layer_rate_kbps * 1000);
       }
       tl_allocation_sum_kbps += layer_rate_kbps;
     }
     RTC_DCHECK_LE(tl_allocation_sum_kbps, expected_allocated_bitrate_kbps);
   }
 }

 std::vector<uint32_t> SimulcastRateAllocator::DefaultTemporalLayerAllocation(
     int bitrate_kbps,
     int max_bitrate_kbps,
     int simulcast_id) const {
   const size_t num_temporal_layers = NumTemporalStreams(simulcast_id);
   std::vector<uint32_t> bitrates;
   for (size_t i = 0; i < num_temporal_layers; ++i) {
     float layer_bitrate =
         bitrate_kbps *
         GetTemporalRateAllocation(
             num_temporal_layers, i,
             rate_control_settings_.Vp8BaseHeavyTl3RateAllocation());
     bitrates.push_back(static_cast<uint32_t>(layer_bitrate + 0.5));
   }

   // Allocation table is of aggregates, transform to individual rates.
   uint32_t sum = 0;
   for (size_t i = 0; i < num_temporal_layers; ++i) {
     uint32_t layer_bitrate = bitrates[i];
     RTC_DCHECK_LE(sum, bitrates[i]);
     bitrates[i] -= sum;
     sum = layer_bitrate;

     if (sum >= static_cast<uint32_t>(bitrate_kbps)) {
       // Sum adds up; any subsequent layers will be 0.
       bitrates.resize(i + 1);
       break;
     }
   }

   return bitrates;
 }

 std::vector<uint32_t>
 SimulcastRateAllocator::ScreenshareTemporalLayerAllocation(
     int bitrate_kbps,
     int max_bitrate_kbps,
     int simulcast_id) const {
   if (simulcast_id > 0) {
     return DefaultTemporalLayerAllocation(bitrate_kbps, max_bitrate_kbps,
                                           simulcast_id);
   }
   std::vector<uint32_t> allocation;
   allocation.push_back(bitrate_kbps);
   if (max_bitrate_kbps > bitrate_kbps)
     allocation.push_back(max_bitrate_kbps - bitrate_kbps);
   return allocation;
 }

 const VideoCodec& webrtc::SimulcastRateAllocator::GetCodec() const {
   return codec_;
 }

 int SimulcastRateAllocator::NumTemporalStreams(size_t simulcast_id) const {
   return std::max<uint8_t>(
       1,
       codec_.codecType == kVideoCodecVP8 && codec_.numberOfSimulcastStreams == 0
           ? codec_.VP8().numberOfTemporalLayers
           : codec_.simulcastStream[simulcast_id].numberOfTemporalLayers);
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2016 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/utility/simulcast_rate_allocator.h"

	#include <stdio.h>

	#include <algorithm>
	#include <cmath>
	#include <cstdint>
	#include <numeric>
	#include <string>
	#include <tuple>
	#include <vector>

	#include "rtc_base/checks.h"
	#include "rtc_base/experiments/rate_control_settings.h"
	#include "system_wrappers/include/field_trial.h"

	namespace webrtc {
	namespace {
	// Ratio allocation between temporal streams:
	// Values as required for the VP8 codec (accumulating).
	static const float
	kLayerRateAllocation[kMaxTemporalStreams][kMaxTemporalStreams] = {
	{1.0f, 1.0f, 1.0f, 1.0f}, // 1 layer
	{0.6f, 1.0f, 1.0f, 1.0f}, // 2 layers {60%, 40%}
	{0.4f, 0.6f, 1.0f, 1.0f}, // 3 layers {40%, 20%, 40%}
	{0.25f, 0.4f, 0.6f, 1.0f} // 4 layers {25%, 15%, 20%, 40%}
	};

	static const float kBaseHeavy3TlRateAllocation[kMaxTemporalStreams] = {
	0.6f, 0.8f, 1.0f, 1.0f // 3 layers {60%, 20%, 20%}
	};

	const uint32_t kLegacyScreenshareTl0BitrateKbps = 200;
	const uint32_t kLegacyScreenshareTl1BitrateKbps = 1000;
	} // namespace

	float SimulcastRateAllocator::GetTemporalRateAllocation(
	int num_layers,
	int temporal_id,
	bool base_heavy_tl3_alloc) {
	RTC_CHECK_GT(num_layers, 0);
	RTC_CHECK_LE(num_layers, kMaxTemporalStreams);
	RTC_CHECK_GE(temporal_id, 0);
	RTC_CHECK_LT(temporal_id, num_layers);
	if (num_layers == 3 && base_heavy_tl3_alloc) {
	return kBaseHeavy3TlRateAllocation[temporal_id];
	}
	return kLayerRateAllocation[num_layers - 1][temporal_id];
	}

	SimulcastRateAllocator::SimulcastRateAllocator(const VideoCodec& codec)
	: codec_(codec),
	stable_rate_settings_(StableTargetRateExperiment::ParseFromFieldTrials()),
	rate_control_settings_(RateControlSettings::ParseFromFieldTrials()) {}

	SimulcastRateAllocator::~SimulcastRateAllocator() = default;

	VideoBitrateAllocation SimulcastRateAllocator::Allocate(
	VideoBitrateAllocationParameters parameters) {
	VideoBitrateAllocation allocated_bitrates;
	DataRate stable_rate = parameters.total_bitrate;
	if (stable_rate_settings_.IsEnabled() &&
	parameters.stable_bitrate > DataRate::Zero()) {
	stable_rate = std::min(parameters.stable_bitrate, parameters.total_bitrate);
	}
	DistributeAllocationToSimulcastLayers(parameters.total_bitrate, stable_rate,
	&allocated_bitrates);
	DistributeAllocationToTemporalLayers(&allocated_bitrates);
	return allocated_bitrates;
	}

	void SimulcastRateAllocator::DistributeAllocationToSimulcastLayers(
	DataRate total_bitrate,
	DataRate stable_bitrate,
	VideoBitrateAllocation* allocated_bitrates) {
	DataRate left_in_total_allocation = total_bitrate;
	DataRate left_in_stable_allocation = stable_bitrate;

	if (codec_.maxBitrate) {
	DataRate max_rate = DataRate::kbps(codec_.maxBitrate);
	left_in_total_allocation = std::min(left_in_total_allocation, max_rate);
	left_in_stable_allocation = std::min(left_in_stable_allocation, max_rate);
	}

	if (codec_.numberOfSimulcastStreams == 0) {
	// No simulcast, just set the target as this has been capped already.
	if (codec_.active) {
	allocated_bitrates->SetBitrate(
	0, 0,
	std::max(DataRate::kbps(codec_.minBitrate), left_in_total_allocation)
	.bps());
	}
	return;
	}

	// Sort the layers by maxFramerate, they might not always be from smallest
	// to biggest
	std::vector<size_t> layer_index(codec_.numberOfSimulcastStreams);
	std::iota(layer_index.begin(), layer_index.end(), 0);
	std::stable_sort(layer_index.begin(), layer_index.end(),
	[this](size_t a, size_t b) {
	return std::tie(codec_.simulcastStream[a].maxBitrate) <
	std::tie(codec_.simulcastStream[b].maxBitrate);
	});

	// Find the first active layer. We don't allocate to inactive layers.
	size_t active_layer = 0;
	for (; active_layer < codec_.numberOfSimulcastStreams; ++active_layer) {
	if (codec_.simulcastStream[layer_index[active_layer]].active) {
	// Found the first active layer.
	break;
	}
	}
	// All streams could be inactive, and nothing more to do.
	if (active_layer == codec_.numberOfSimulcastStreams) {
	return;
	}

	// Always allocate enough bitrate for the minimum bitrate of the first
	// active layer. Suspending below min bitrate is controlled outside the
	// codec implementation and is not overridden by this.
	DataRate min_rate = DataRate::kbps(
	codec_.simulcastStream[layer_index[active_layer]].minBitrate);
	left_in_total_allocation = std::max(left_in_total_allocation, min_rate);
	left_in_stable_allocation = std::max(left_in_stable_allocation, min_rate);

	// Begin by allocating bitrate to simulcast streams, putting all bitrate in
	// temporal layer 0. We'll then distribute this bitrate, across potential
	// temporal layers, when stream allocation is done.

	bool first_allocation = false;
	if (stream_enabled_.empty()) {
	// First time allocating, this means we should not include hysteresis in
	// case this is a reconfiguration of an existing enabled stream.
	first_allocation = true;
	stream_enabled_.resize(codec_.numberOfSimulcastStreams, false);
	}

	size_t top_active_layer = active_layer;
	// Allocate up to the target bitrate for each active simulcast layer.
	for (; active_layer < codec_.numberOfSimulcastStreams; ++active_layer) {
	const SimulcastStream& stream =
	codec_.simulcastStream[layer_index[active_layer]];
	if (!stream.active) {
	stream_enabled_[layer_index[active_layer]] = false;
	continue;
	}
	// If we can't allocate to the current layer we can't allocate to higher
	// layers because they require a higher minimum bitrate.
	DataRate min_bitrate = DataRate::kbps(stream.minBitrate);
	DataRate target_bitrate = DataRate::kbps(stream.targetBitrate);
	double hysteresis_factor =
	codec_.mode == VideoCodecMode::kRealtimeVideo
	? stable_rate_settings_.GetVideoHysteresisFactor()
	: stable_rate_settings_.GetScreenshareHysteresisFactor();
	if (!first_allocation && !stream_enabled_[layer_index[active_layer]]) {
	min_bitrate = std::min(hysteresis_factor * min_bitrate, target_bitrate);
	}
	if (left_in_stable_allocation < min_bitrate) {
	allocated_bitrates->set_bw_limited(true);
	break;
	}

	// We are allocating to this layer so it is the current active allocation.
	top_active_layer = layer_index[active_layer];
	stream_enabled_[layer_index[active_layer]] = true;
	DataRate layer_rate = std::min(left_in_total_allocation, target_bitrate);
	allocated_bitrates->SetBitrate(layer_index[active_layer], 0,
	layer_rate.bps());
	left_in_total_allocation -= layer_rate;
	left_in_stable_allocation -=
	std::min(left_in_stable_allocation, target_bitrate);
	}

	// All layers above this one are not active.
	for (; active_layer < codec_.numberOfSimulcastStreams; ++active_layer) {
	stream_enabled_[layer_index[active_layer]] = false;
	}

	// Next, try allocate remaining bitrate, up to max bitrate, in top active
	// stream.
	// TODO(sprang): Allocate up to max bitrate for all layers once we have a
	// better idea of possible performance implications.
	if (left_in_total_allocation > DataRate::Zero()) {
	const SimulcastStream& stream = codec_.simulcastStream[top_active_layer];
	DataRate initial_layer_rate =
	DataRate::bps(allocated_bitrates->GetSpatialLayerSum(top_active_layer));
	DataRate additional_allocation =
	std::min(left_in_total_allocation,
	DataRate::kbps(stream.maxBitrate) - initial_layer_rate);
	allocated_bitrates->SetBitrate(
	top_active_layer, 0,
	(initial_layer_rate + additional_allocation).bps());
	}
	}

	void SimulcastRateAllocator::DistributeAllocationToTemporalLayers(
	VideoBitrateAllocation* allocated_bitrates_bps) const {
	const int num_spatial_streams =
	std::max(1, static_cast<int>(codec_.numberOfSimulcastStreams));

	// Finally, distribute the bitrate for the simulcast streams across the
	// available temporal layers.
	for (int simulcast_id = 0; simulcast_id < num_spatial_streams;
	++simulcast_id) {
	uint32_t target_bitrate_kbps =
	allocated_bitrates_bps->GetBitrate(simulcast_id, 0) / 1000;
	if (target_bitrate_kbps == 0) {
	continue;
	}

	const uint32_t expected_allocated_bitrate_kbps = target_bitrate_kbps;
	RTC_DCHECK_EQ(
	target_bitrate_kbps,
	allocated_bitrates_bps->GetSpatialLayerSum(simulcast_id) / 1000);
	const int num_temporal_streams = NumTemporalStreams(simulcast_id);
	uint32_t max_bitrate_kbps;
	// Legacy temporal-layered only screenshare, or simulcast screenshare
	// with legacy mode for simulcast stream 0.
	const bool conference_screenshare_mode =
	codec_.mode == VideoCodecMode::kScreensharing &&
	((num_spatial_streams == 1 && num_temporal_streams == 2) \|\| // Legacy.
	(num_spatial_streams > 1 && simulcast_id == 0 &&
	num_temporal_streams == 2)); // Simulcast.
	if (conference_screenshare_mode) {
	// TODO(holmer): This is a "temporary" hack for screensharing, where we
	// interpret the startBitrate as the encoder target bitrate. This is
	// to allow for a different max bitrate, so if the codec can't meet
	// the target we still allow it to overshoot up to the max before dropping
	// frames. This hack should be improved.
	max_bitrate_kbps =
	std::min(kLegacyScreenshareTl1BitrateKbps, target_bitrate_kbps);
	target_bitrate_kbps =
	std::min(kLegacyScreenshareTl0BitrateKbps, target_bitrate_kbps);
	} else if (num_spatial_streams == 1) {
	max_bitrate_kbps = codec_.maxBitrate;
	} else {
	max_bitrate_kbps = codec_.simulcastStream[simulcast_id].maxBitrate;
	}

	std::vector<uint32_t> tl_allocation;
	if (num_temporal_streams == 1) {
	tl_allocation.push_back(target_bitrate_kbps);
	} else {
	if (conference_screenshare_mode) {
	tl_allocation = ScreenshareTemporalLayerAllocation(
	target_bitrate_kbps, max_bitrate_kbps, simulcast_id);
	} else {
	tl_allocation = DefaultTemporalLayerAllocation(
	target_bitrate_kbps, max_bitrate_kbps, simulcast_id);
	}
	}
	RTC_DCHECK_GT(tl_allocation.size(), 0);
	RTC_DCHECK_LE(tl_allocation.size(), num_temporal_streams);

	uint64_t tl_allocation_sum_kbps = 0;
	for (size_t tl_index = 0; tl_index < tl_allocation.size(); ++tl_index) {
	uint32_t layer_rate_kbps = tl_allocation[tl_index];
	if (layer_rate_kbps > 0) {
	allocated_bitrates_bps->SetBitrate(simulcast_id, tl_index,
	layer_rate_kbps * 1000);
	}
	tl_allocation_sum_kbps += layer_rate_kbps;
	}
	RTC_DCHECK_LE(tl_allocation_sum_kbps, expected_allocated_bitrate_kbps);
	}
	}

	std::vector<uint32_t> SimulcastRateAllocator::DefaultTemporalLayerAllocation(
	int bitrate_kbps,
	int max_bitrate_kbps,
	int simulcast_id) const {
	const size_t num_temporal_layers = NumTemporalStreams(simulcast_id);
	std::vector<uint32_t> bitrates;
	for (size_t i = 0; i < num_temporal_layers; ++i) {
	float layer_bitrate =
	bitrate_kbps *
	GetTemporalRateAllocation(
	num_temporal_layers, i,
	rate_control_settings_.Vp8BaseHeavyTl3RateAllocation());
	bitrates.push_back(static_cast<uint32_t>(layer_bitrate + 0.5));
	}

	// Allocation table is of aggregates, transform to individual rates.
	uint32_t sum = 0;
	for (size_t i = 0; i < num_temporal_layers; ++i) {
	uint32_t layer_bitrate = bitrates[i];
	RTC_DCHECK_LE(sum, bitrates[i]);
	bitrates[i] -= sum;
	sum = layer_bitrate;

	if (sum >= static_cast<uint32_t>(bitrate_kbps)) {
	// Sum adds up; any subsequent layers will be 0.
	bitrates.resize(i + 1);
	break;
	}
	}

	return bitrates;
	}

	std::vector<uint32_t>
	SimulcastRateAllocator::ScreenshareTemporalLayerAllocation(
	int bitrate_kbps,
	int max_bitrate_kbps,
	int simulcast_id) const {
	if (simulcast_id > 0) {
	return DefaultTemporalLayerAllocation(bitrate_kbps, max_bitrate_kbps,
	simulcast_id);
	}
	std::vector<uint32_t> allocation;
	allocation.push_back(bitrate_kbps);
	if (max_bitrate_kbps > bitrate_kbps)
	allocation.push_back(max_bitrate_kbps - bitrate_kbps);
	return allocation;
	}

	const VideoCodec& webrtc::SimulcastRateAllocator::GetCodec() const {
	return codec_;
	}

	int SimulcastRateAllocator::NumTemporalStreams(size_t simulcast_id) const {
	return std::max<uint8_t>(
	1,
	codec_.codecType == kVideoCodecVP8 && codec_.numberOfSimulcastStreams == 0
	? codec_.VP8().numberOfTemporalLayers
	: codec_.simulcastStream[simulcast_id].numberOfTemporalLayers);
	}

	} // namespace webrtc