media/engine/simulcast.cc

/*
 *  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].num_temporal_layers = kDefaultConferenceNumberOfTemporalLayers[s];
    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].num_temporal_layers = 2;

  // 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].num_temporal_layers = 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;
  }

  // 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