media/engine/simulcast.cc - src.git - Git at Google

 /*
  *  Copyright (c) 2014 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 <stdio.h>
 #include <algorithm>
 #include <string>

 #include "media/base/streamparams.h"
 #include "media/engine/constants.h"
 #include "media/engine/simulcast.h"
 #include "rtc_base/arraysize.h"
 #include "rtc_base/logging.h"
 #include "system_wrappers/include/field_trial.h"

 namespace cricket {

 struct SimulcastFormat {
   int width;
   int height;
   // The maximum number of simulcast layers can be used for
   // resolutions at |widthxheigh|.
   size_t max_layers;
   // The maximum bitrate for encoding stream at |widthxheight|, when we are
   // not sending the next higher spatial stream.
   int max_bitrate_kbps;
   // The target bitrate for encoding stream at |widthxheight|, when this layer
   // is not the highest layer (i.e., when we are sending another higher spatial
   // stream).
   int target_bitrate_kbps;
   // The minimum bitrate needed for encoding stream at |widthxheight|.
   int min_bitrate_kbps;
 };

 // These tables describe from which resolution we can use how many
 // simulcast layers at what bitrates (maximum, target, and minimum).
 // Important!! Keep this table from high resolution to low resolution.
 const SimulcastFormat kSimulcastFormats[] = {
   {1920, 1080, 3, 5000, 4000, 800},
   {1280, 720, 3,  2500, 2500, 600},
   {960, 540, 3, 900, 900, 450},
   {640, 360, 2, 700, 500, 150},
   {480, 270, 2, 450, 350, 150},
   {320, 180, 1, 200, 150, 30},
   {0, 0, 1, 200, 150, 30}
 };

 const int kMaxScreenshareSimulcastLayers = 2;

 // Multiway: Number of temporal layers for each simulcast stream, for maximum
 // possible number of simulcast streams |kMaxSimulcastStreams|. The array
 // goes from lowest resolution at position 0 to highest resolution.
 // For example, first three elements correspond to say: QVGA, VGA, WHD.
 static const int
     kDefaultConferenceNumberOfTemporalLayers[webrtc::kMaxSimulcastStreams] =
     {3, 3, 3, 3};

 int FindSimulcastFormatIndex(int width, int height) {
   RTC_DCHECK_GE(width, 0);
   RTC_DCHECK_GE(height, 0);
   for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
     if (width * height >=
         kSimulcastFormats[i].width * kSimulcastFormats[i].height) {
       return i;
     }
   }
   RTC_NOTREACHED();
   return -1;
 }

 int FindSimulcastFormatIndex(int width, int height, size_t max_layers) {
   RTC_DCHECK_GE(width, 0);
   RTC_DCHECK_GE(height, 0);
   RTC_DCHECK_GT(max_layers, 0);
   for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
     if (width * height >=
             kSimulcastFormats[i].width * kSimulcastFormats[i].height &&
         max_layers == kSimulcastFormats[i].max_layers) {
       return i;
     }
   }
   RTC_NOTREACHED();
   return -1;
 }

 // Simulcast stream width and height must both be dividable by
 // |2 ^ simulcast_layers - 1|.
 int NormalizeSimulcastSize(int size, size_t simulcast_layers) {
   const int base2_exponent = static_cast<int>(simulcast_layers) - 1;
   return ((size >> base2_exponent) << base2_exponent);
 }

 size_t FindSimulcastMaxLayers(int width, int height) {
   int index = FindSimulcastFormatIndex(width, height);
   return kSimulcastFormats[index].max_layers;
 }

 int FindSimulcastMaxBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
   return kSimulcastFormats[format_index].max_bitrate_kbps * 1000;
 }

 int FindSimulcastTargetBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
   return kSimulcastFormats[format_index].target_bitrate_kbps * 1000;
 }

 int FindSimulcastMinBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
   return kSimulcastFormats[format_index].min_bitrate_kbps * 1000;
 }

 void SlotSimulcastMaxResolution(size_t max_layers, int* width, int* height) {
   int index = FindSimulcastFormatIndex(*width, *height, max_layers);
   *width = kSimulcastFormats[index].width;
   *height = kSimulcastFormats[index].height;
   RTC_LOG(LS_INFO) << "SlotSimulcastMaxResolution to width:" << *width
                    << " height:" << *height;
 }

 void BoostMaxSimulcastLayer(int max_bitrate_bps,
                             std::vector<webrtc::VideoStream>* layers) {
   // Spend additional bits to boost the max layer.
   int bitrate_left_bps = max_bitrate_bps - GetTotalMaxBitrateBps(*layers);
   if (bitrate_left_bps > 0) {
     layers->back().max_bitrate_bps += bitrate_left_bps;
   }
 }

 int GetTotalMaxBitrateBps(const std::vector<webrtc::VideoStream>& layers) {
   int total_max_bitrate_bps = 0;
   for (size_t s = 0; s < layers.size() - 1; ++s) {
     total_max_bitrate_bps += layers[s].target_bitrate_bps;
   }
   total_max_bitrate_bps += layers.back().max_bitrate_bps;
   return total_max_bitrate_bps;
 }

 std::vector<webrtc::VideoStream> GetSimulcastConfig(size_t max_layers,
                                                     int width,
                                                     int height,
                                                     int max_bitrate_bps,
                                                     double bitrate_priority,
                                                     int max_qp,
                                                     int max_framerate,
                                                     bool is_screenshare) {
   if (is_screenshare) {
     return GetScreenshareLayers(max_layers, width, height, max_bitrate_bps,
                                 bitrate_priority, max_qp, max_framerate,
                                 ScreenshareSimulcastFieldTrialEnabled());
   } else {
     return GetNormalSimulcastLayers(max_layers, width, height, max_bitrate_bps,
                                     bitrate_priority, max_qp, max_framerate);
   }
 }

 std::vector<webrtc::VideoStream> GetNormalSimulcastLayers(
     size_t max_layers,
     int width,
     int height,
     int max_bitrate_bps,
     double bitrate_priority,
     int max_qp,
     int max_framerate) {
   // TODO(bugs.webrtc.org/8785): Currently if the resolution isn't large enough
   // (defined in kSimulcastFormats) we scale down the number of simulcast
   // layers. Consider changing this so that the application can have more
   // control over exactly how many simulcast layers are used.
   size_t num_simulcast_layers = FindSimulcastMaxLayers(width, height);
   if (num_simulcast_layers > max_layers) {
     // TODO(bugs.webrtc.org/8486): This scales down the resolution if the
     // number of simulcast layers created by the application isn't sufficient
     // (defined in kSimulcastFormats). For example if the input frame's
     // resolution is HD, but there are only 2 simulcast layers, the
     // resolution gets scaled down to VGA. Consider taking this logic out to
     // allow the application more control over the resolutions.
     SlotSimulcastMaxResolution(max_layers, &width, &height);
     num_simulcast_layers = max_layers;
   }
   std::vector<webrtc::VideoStream> layers(num_simulcast_layers);

   // Format width and height has to be divisible by |2 ^ num_simulcast_layers -
   // 1|.
   width = NormalizeSimulcastSize(width, num_simulcast_layers);
   height = NormalizeSimulcastSize(height, num_simulcast_layers);
   // Add simulcast streams, from highest resolution (|s| = num_simulcast_layers
   // -1) to lowest resolution at |s| = 0.
   for (size_t s = num_simulcast_layers - 1;; --s) {
     layers[s].width = width;
     layers[s].height = height;
     // TODO(pbos): Fill actual temporal-layer bitrate thresholds.
     layers[s].max_qp = max_qp;
     layers[s].temporal_layer_thresholds_bps.resize(
         kDefaultConferenceNumberOfTemporalLayers[s] - 1);
     layers[s].max_bitrate_bps = FindSimulcastMaxBitrateBps(width, height);
     layers[s].target_bitrate_bps = FindSimulcastTargetBitrateBps(width, height);
     layers[s].min_bitrate_bps = FindSimulcastMinBitrateBps(width, height);
     layers[s].max_framerate = max_framerate;

     width /= 2;
     height /= 2;

     if (s == 0) {
       break;
     }
   }
   // If there is bitrate leftover, give it to the largest layer.
   BoostMaxSimulcastLayer(max_bitrate_bps, &layers);
   // Currently the relative bitrate priority of the sender is controlled by
   // the value of the lowest VideoStream.
   // TODO(bugs.webrtc.org/8630): The web specification describes being able to
   // control relative bitrate for each individual simulcast layer, but this
   // is currently just implemented per rtp sender.
   layers[0].bitrate_priority = bitrate_priority;
   return layers;
 }

 std::vector<webrtc::VideoStream> GetScreenshareLayers(
     size_t max_layers,
     int width,
     int height,
     int max_bitrate_bps,
     double bitrate_priority,
     int max_qp,
     int max_framerate,
     bool screenshare_simulcast_enabled) {
   auto max_screenshare_layers =
       screenshare_simulcast_enabled ? kMaxScreenshareSimulcastLayers : 1;
   size_t num_simulcast_layers =
       std::min<int>(max_layers, max_screenshare_layers);

   std::vector<webrtc::VideoStream> layers(num_simulcast_layers);
   ScreenshareLayerConfig config = ScreenshareLayerConfig::GetDefault();
   // For legacy screenshare in conference mode, tl0 and tl1 bitrates are
   // piggybacked on the VideoCodec struct as target and max bitrates,
   // respectively. See eg. webrtc::VP8EncoderImpl::SetRates().
   layers[0].width = width;
   layers[0].height = height;
   layers[0].max_qp = max_qp;
   layers[0].max_framerate = 5;
   layers[0].min_bitrate_bps = kMinVideoBitrateBps;
   layers[0].target_bitrate_bps = config.tl0_bitrate_kbps * 1000;
   layers[0].max_bitrate_bps = config.tl1_bitrate_kbps * 1000;
   layers[0].temporal_layer_thresholds_bps.clear();
   layers[0].temporal_layer_thresholds_bps.push_back(config.tl0_bitrate_kbps *
                                                     1000);

   // With simulcast enabled, add another spatial layer. This one will have a
   // more normal layout, with the regular 3 temporal layer pattern and no fps
   // restrictions. The base simulcast layer will still use legacy setup.
   if (num_simulcast_layers == kMaxScreenshareSimulcastLayers) {
     // Add optional upper simulcast layer.
     // Lowest temporal layers of a 3 layer setup will have 40% of the total
     // bitrate allocation for that simulcast layer. Make sure the gap between
     // the target of the lower simulcast layer and first temporal layer of the
     // higher one is at most 2x the bitrate, so that upswitching is not hampered
     // by stalled bitrate estimates.
     int max_bitrate_bps = 2 * ((layers[0].target_bitrate_bps * 10) / 4);
     // Cap max bitrate so it isn't overly high for the given resolution.
     max_bitrate_bps = std::min<int>(max_bitrate_bps,
                                     FindSimulcastMaxBitrateBps(width, height));

     layers[1].width = width;
     layers[1].height = height;
     layers[1].max_qp = max_qp;
     layers[1].max_framerate = max_framerate;
     // Three temporal layers means two thresholds.
     layers[1].temporal_layer_thresholds_bps.resize(2);
     layers[1].min_bitrate_bps = layers[0].target_bitrate_bps * 2;
     layers[1].target_bitrate_bps = max_bitrate_bps;
     layers[1].max_bitrate_bps = max_bitrate_bps;
   }

   BoostMaxSimulcastLayer(max_bitrate_bps, &layers);
   // The bitrate priority currently implemented on a per-sender level, so we
   // just set it for the first simulcast layer.
   layers[0].bitrate_priority = bitrate_priority;
   return layers;
 }

 static const int kScreenshareMinBitrateKbps = 50;
 static const int kScreenshareMaxBitrateKbps = 6000;
 static const int kScreenshareDefaultTl0BitrateKbps = 200;
 static const int kScreenshareDefaultTl1BitrateKbps = 1000;

 static const char* kScreenshareLayerFieldTrialName =
     "WebRTC-ScreenshareLayerRates";
 static const char* kSimulcastScreenshareFieldTrialName =
     "WebRTC-SimulcastScreenshare";

 ScreenshareLayerConfig::ScreenshareLayerConfig(int tl0_bitrate, int tl1_bitrate)
     : tl0_bitrate_kbps(tl0_bitrate), tl1_bitrate_kbps(tl1_bitrate) {
 }

 ScreenshareLayerConfig ScreenshareLayerConfig::GetDefault() {
   std::string group =
       webrtc::field_trial::FindFullName(kScreenshareLayerFieldTrialName);

   ScreenshareLayerConfig config(kScreenshareDefaultTl0BitrateKbps,
                                 kScreenshareDefaultTl1BitrateKbps);
   if (!group.empty() && !FromFieldTrialGroup(group, &config)) {
     RTC_LOG(LS_WARNING) << "Unable to parse WebRTC-ScreenshareLayerRates"
                            " field trial group: '"
                         << group << "'.";
   }
   return config;
 }

 bool ScreenshareLayerConfig::FromFieldTrialGroup(
     const std::string& group,
     ScreenshareLayerConfig* config) {
   // Parse field trial group name, containing bitrates for tl0 and tl1.
   int tl0_bitrate;
   int tl1_bitrate;
   if (sscanf(group.c_str(), "%d-%d", &tl0_bitrate, &tl1_bitrate) != 2) {
     return false;
   }

   // Sanity check.
   if (tl0_bitrate < kScreenshareMinBitrateKbps ||
       tl0_bitrate > kScreenshareMaxBitrateKbps ||
       tl1_bitrate < kScreenshareMinBitrateKbps ||
       tl1_bitrate > kScreenshareMaxBitrateKbps || tl0_bitrate > tl1_bitrate) {
     return false;
   }

   config->tl0_bitrate_kbps = tl0_bitrate;
   config->tl1_bitrate_kbps = tl1_bitrate;

   return true;
 }

 bool ScreenshareSimulcastFieldTrialEnabled() {
   return webrtc::field_trial::IsEnabled(kSimulcastScreenshareFieldTrialName);
 }

 }  // namespace cricket
	/*
	* Copyright (c) 2014 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 <stdio.h>
	#include <algorithm>
	#include <string>

	#include "media/base/streamparams.h"
	#include "media/engine/constants.h"
	#include "media/engine/simulcast.h"
	#include "rtc_base/arraysize.h"
	#include "rtc_base/logging.h"
	#include "system_wrappers/include/field_trial.h"

	namespace cricket {

	struct SimulcastFormat {
	int width;
	int height;
	// The maximum number of simulcast layers can be used for
	// resolutions at \|widthxheigh\|.
	size_t max_layers;
	// The maximum bitrate for encoding stream at \|widthxheight\|, when we are
	// not sending the next higher spatial stream.
	int max_bitrate_kbps;
	// The target bitrate for encoding stream at \|widthxheight\|, when this layer
	// is not the highest layer (i.e., when we are sending another higher spatial
	// stream).
	int target_bitrate_kbps;
	// The minimum bitrate needed for encoding stream at \|widthxheight\|.
	int min_bitrate_kbps;
	};

	// These tables describe from which resolution we can use how many
	// simulcast layers at what bitrates (maximum, target, and minimum).
	// Important!! Keep this table from high resolution to low resolution.
	const SimulcastFormat kSimulcastFormats[] = {
	{1920, 1080, 3, 5000, 4000, 800},
	{1280, 720, 3, 2500, 2500, 600},
	{960, 540, 3, 900, 900, 450},
	{640, 360, 2, 700, 500, 150},
	{480, 270, 2, 450, 350, 150},
	{320, 180, 1, 200, 150, 30},
	{0, 0, 1, 200, 150, 30}
	};

	const int kMaxScreenshareSimulcastLayers = 2;

	// Multiway: Number of temporal layers for each simulcast stream, for maximum
	// possible number of simulcast streams \|kMaxSimulcastStreams\|. The array
	// goes from lowest resolution at position 0 to highest resolution.
	// For example, first three elements correspond to say: QVGA, VGA, WHD.
	static const int
	kDefaultConferenceNumberOfTemporalLayers[webrtc::kMaxSimulcastStreams] =
	{3, 3, 3, 3};

	int FindSimulcastFormatIndex(int width, int height) {
	RTC_DCHECK_GE(width, 0);
	RTC_DCHECK_GE(height, 0);
	for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
	if (width * height >=
	kSimulcastFormats[i].width * kSimulcastFormats[i].height) {
	return i;
	}
	}
	RTC_NOTREACHED();
	return -1;
	}

	int FindSimulcastFormatIndex(int width, int height, size_t max_layers) {
	RTC_DCHECK_GE(width, 0);
	RTC_DCHECK_GE(height, 0);
	RTC_DCHECK_GT(max_layers, 0);
	for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
	if (width * height >=
	kSimulcastFormats[i].width * kSimulcastFormats[i].height &&
	max_layers == kSimulcastFormats[i].max_layers) {
	return i;
	}
	}
	RTC_NOTREACHED();
	return -1;
	}

	// Simulcast stream width and height must both be dividable by
	// \|2 ^ simulcast_layers - 1\|.
	int NormalizeSimulcastSize(int size, size_t simulcast_layers) {
	const int base2_exponent = static_cast<int>(simulcast_layers) - 1;
	return ((size >> base2_exponent) << base2_exponent);
	}

	size_t FindSimulcastMaxLayers(int width, int height) {
	int index = FindSimulcastFormatIndex(width, height);
	return kSimulcastFormats[index].max_layers;
	}

	int FindSimulcastMaxBitrateBps(int width, int height) {
	const int format_index = FindSimulcastFormatIndex(width, height);
	return kSimulcastFormats[format_index].max_bitrate_kbps * 1000;
	}

	int FindSimulcastTargetBitrateBps(int width, int height) {
	const int format_index = FindSimulcastFormatIndex(width, height);
	return kSimulcastFormats[format_index].target_bitrate_kbps * 1000;
	}

	int FindSimulcastMinBitrateBps(int width, int height) {
	const int format_index = FindSimulcastFormatIndex(width, height);
	return kSimulcastFormats[format_index].min_bitrate_kbps * 1000;
	}

	void SlotSimulcastMaxResolution(size_t max_layers, int* width, int* height) {
	int index = FindSimulcastFormatIndex(width, height, max_layers);
	*width = kSimulcastFormats[index].width;
	*height = kSimulcastFormats[index].height;
	RTC_LOG(LS_INFO) << "SlotSimulcastMaxResolution to width:" << *width
	<< " height:" << *height;
	}

	void BoostMaxSimulcastLayer(int max_bitrate_bps,
	std::vector<webrtc::VideoStream>* layers) {
	// Spend additional bits to boost the max layer.
	int bitrate_left_bps = max_bitrate_bps - GetTotalMaxBitrateBps(*layers);
	if (bitrate_left_bps > 0) {
	layers->back().max_bitrate_bps += bitrate_left_bps;
	}
	}

	int GetTotalMaxBitrateBps(const std::vector<webrtc::VideoStream>& layers) {
	int total_max_bitrate_bps = 0;
	for (size_t s = 0; s < layers.size() - 1; ++s) {
	total_max_bitrate_bps += layers[s].target_bitrate_bps;
	}
	total_max_bitrate_bps += layers.back().max_bitrate_bps;
	return total_max_bitrate_bps;
	}

	std::vector<webrtc::VideoStream> GetSimulcastConfig(size_t max_layers,
	int width,
	int height,
	int max_bitrate_bps,
	double bitrate_priority,
	int max_qp,
	int max_framerate,
	bool is_screenshare) {
	if (is_screenshare) {
	return GetScreenshareLayers(max_layers, width, height, max_bitrate_bps,
	bitrate_priority, max_qp, max_framerate,
	ScreenshareSimulcastFieldTrialEnabled());
	} else {
	return GetNormalSimulcastLayers(max_layers, width, height, max_bitrate_bps,
	bitrate_priority, max_qp, max_framerate);
	}
	}

	std::vector<webrtc::VideoStream> GetNormalSimulcastLayers(
	size_t max_layers,
	int width,
	int height,
	int max_bitrate_bps,
	double bitrate_priority,
	int max_qp,
	int max_framerate) {
	// TODO(bugs.webrtc.org/8785): Currently if the resolution isn't large enough
	// (defined in kSimulcastFormats) we scale down the number of simulcast
	// layers. Consider changing this so that the application can have more
	// control over exactly how many simulcast layers are used.
	size_t num_simulcast_layers = FindSimulcastMaxLayers(width, height);
	if (num_simulcast_layers > max_layers) {
	// TODO(bugs.webrtc.org/8486): This scales down the resolution if the
	// number of simulcast layers created by the application isn't sufficient
	// (defined in kSimulcastFormats). For example if the input frame's
	// resolution is HD, but there are only 2 simulcast layers, the
	// resolution gets scaled down to VGA. Consider taking this logic out to
	// allow the application more control over the resolutions.
	SlotSimulcastMaxResolution(max_layers, &width, &height);
	num_simulcast_layers = max_layers;
	}
	std::vector<webrtc::VideoStream> layers(num_simulcast_layers);

	// Format width and height has to be divisible by \|2 ^ num_simulcast_layers -
	// 1\|.
	width = NormalizeSimulcastSize(width, num_simulcast_layers);
	height = NormalizeSimulcastSize(height, num_simulcast_layers);
	// Add simulcast streams, from highest resolution (\|s\| = num_simulcast_layers
	// -1) to lowest resolution at \|s\| = 0.
	for (size_t s = num_simulcast_layers - 1;; --s) {
	layers[s].width = width;
	layers[s].height = height;
	// TODO(pbos): Fill actual temporal-layer bitrate thresholds.
	layers[s].max_qp = max_qp;
	layers[s].temporal_layer_thresholds_bps.resize(
	kDefaultConferenceNumberOfTemporalLayers[s] - 1);
	layers[s].max_bitrate_bps = FindSimulcastMaxBitrateBps(width, height);
	layers[s].target_bitrate_bps = FindSimulcastTargetBitrateBps(width, height);
	layers[s].min_bitrate_bps = FindSimulcastMinBitrateBps(width, height);
	layers[s].max_framerate = max_framerate;

	width /= 2;
	height /= 2;

	if (s == 0) {
	break;
	}
	}
	// If there is bitrate leftover, give it to the largest layer.
	BoostMaxSimulcastLayer(max_bitrate_bps, &layers);
	// Currently the relative bitrate priority of the sender is controlled by
	// the value of the lowest VideoStream.
	// TODO(bugs.webrtc.org/8630): The web specification describes being able to
	// control relative bitrate for each individual simulcast layer, but this
	// is currently just implemented per rtp sender.
	layers[0].bitrate_priority = bitrate_priority;
	return layers;
	}

	std::vector<webrtc::VideoStream> GetScreenshareLayers(
	size_t max_layers,
	int width,
	int height,
	int max_bitrate_bps,
	double bitrate_priority,
	int max_qp,
	int max_framerate,
	bool screenshare_simulcast_enabled) {
	auto max_screenshare_layers =
	screenshare_simulcast_enabled ? kMaxScreenshareSimulcastLayers : 1;
	size_t num_simulcast_layers =
	std::min<int>(max_layers, max_screenshare_layers);

	std::vector<webrtc::VideoStream> layers(num_simulcast_layers);
	ScreenshareLayerConfig config = ScreenshareLayerConfig::GetDefault();
	// For legacy screenshare in conference mode, tl0 and tl1 bitrates are
	// piggybacked on the VideoCodec struct as target and max bitrates,
	// respectively. See eg. webrtc::VP8EncoderImpl::SetRates().
	layers[0].width = width;
	layers[0].height = height;
	layers[0].max_qp = max_qp;
	layers[0].max_framerate = 5;
	layers[0].min_bitrate_bps = kMinVideoBitrateBps;
	layers[0].target_bitrate_bps = config.tl0_bitrate_kbps * 1000;
	layers[0].max_bitrate_bps = config.tl1_bitrate_kbps * 1000;
	layers[0].temporal_layer_thresholds_bps.clear();
	layers[0].temporal_layer_thresholds_bps.push_back(config.tl0_bitrate_kbps *
	1000);

	// With simulcast enabled, add another spatial layer. This one will have a
	// more normal layout, with the regular 3 temporal layer pattern and no fps
	// restrictions. The base simulcast layer will still use legacy setup.
	if (num_simulcast_layers == kMaxScreenshareSimulcastLayers) {
	// Add optional upper simulcast layer.
	// Lowest temporal layers of a 3 layer setup will have 40% of the total
	// bitrate allocation for that simulcast layer. Make sure the gap between
	// the target of the lower simulcast layer and first temporal layer of the
	// higher one is at most 2x the bitrate, so that upswitching is not hampered
	// by stalled bitrate estimates.
	int max_bitrate_bps = 2 * ((layers[0].target_bitrate_bps * 10) / 4);
	// Cap max bitrate so it isn't overly high for the given resolution.
	max_bitrate_bps = std::min<int>(max_bitrate_bps,
	FindSimulcastMaxBitrateBps(width, height));

	layers[1].width = width;
	layers[1].height = height;
	layers[1].max_qp = max_qp;
	layers[1].max_framerate = max_framerate;
	// Three temporal layers means two thresholds.
	layers[1].temporal_layer_thresholds_bps.resize(2);
	layers[1].min_bitrate_bps = layers[0].target_bitrate_bps * 2;
	layers[1].target_bitrate_bps = max_bitrate_bps;
	layers[1].max_bitrate_bps = max_bitrate_bps;
	}

	BoostMaxSimulcastLayer(max_bitrate_bps, &layers);
	// The bitrate priority currently implemented on a per-sender level, so we
	// just set it for the first simulcast layer.
	layers[0].bitrate_priority = bitrate_priority;
	return layers;
	}

	static const int kScreenshareMinBitrateKbps = 50;
	static const int kScreenshareMaxBitrateKbps = 6000;
	static const int kScreenshareDefaultTl0BitrateKbps = 200;
	static const int kScreenshareDefaultTl1BitrateKbps = 1000;

	static const char* kScreenshareLayerFieldTrialName =
	"WebRTC-ScreenshareLayerRates";
	static const char* kSimulcastScreenshareFieldTrialName =
	"WebRTC-SimulcastScreenshare";

	ScreenshareLayerConfig::ScreenshareLayerConfig(int tl0_bitrate, int tl1_bitrate)
	: tl0_bitrate_kbps(tl0_bitrate), tl1_bitrate_kbps(tl1_bitrate) {
	}

	ScreenshareLayerConfig ScreenshareLayerConfig::GetDefault() {
	std::string group =
	webrtc::field_trial::FindFullName(kScreenshareLayerFieldTrialName);

	ScreenshareLayerConfig config(kScreenshareDefaultTl0BitrateKbps,
	kScreenshareDefaultTl1BitrateKbps);
	if (!group.empty() && !FromFieldTrialGroup(group, &config)) {
	RTC_LOG(LS_WARNING) << "Unable to parse WebRTC-ScreenshareLayerRates"
	" field trial group: '"
	<< group << "'.";
	}
	return config;
	}

	bool ScreenshareLayerConfig::FromFieldTrialGroup(
	const std::string& group,
	ScreenshareLayerConfig* config) {
	// Parse field trial group name, containing bitrates for tl0 and tl1.
	int tl0_bitrate;
	int tl1_bitrate;
	if (sscanf(group.c_str(), "%d-%d", &tl0_bitrate, &tl1_bitrate) != 2) {
	return false;
	}

	// Sanity check.
	if (tl0_bitrate < kScreenshareMinBitrateKbps \|\|
	tl0_bitrate > kScreenshareMaxBitrateKbps \|\|
	tl1_bitrate < kScreenshareMinBitrateKbps \|\|
	tl1_bitrate > kScreenshareMaxBitrateKbps \|\| tl0_bitrate > tl1_bitrate) {
	return false;
	}

	config->tl0_bitrate_kbps = tl0_bitrate;
	config->tl1_bitrate_kbps = tl1_bitrate;

	return true;
	}

	bool ScreenshareSimulcastFieldTrialEnabled() {
	return webrtc::field_trial::IsEnabled(kSimulcastScreenshareFieldTrialName);
	}

	} // namespace cricket