Add experimental simulcast screen content mode

webrtc/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 "webrtc/base/arraysize.h"
 #include "webrtc/base/common.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/media/base/streamparams.h"
+#include "webrtc/media/engine/constants.h"
 #include "webrtc/media/engine/simulcast.h"
 #include "webrtc/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|.
@@ skipping 15 matching lines @@
 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 kDefaultScreenshareSimulcastStreams = 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};
 
 void GetSimulcastSsrcs(const StreamParams& sp, std::vector<uint32_t>* ssrcs) {
   const SsrcGroup* sim_group = sp.get_ssrc_group(kSimSsrcGroupSemantics);
@@ skipping 10 matching lines @@
     int temp = *width;
     *width = *height;
     *height = temp;
   }
 }
 
 int FindSimulcastFormatIndex(int width, int height) {
   MaybeExchangeWidthHeight(&width, &height);
 
   for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
-    if (width >= kSimulcastFormats[i].width &&
-        height >= kSimulcastFormats[i].height) {
+    if (width * height >=
+        kSimulcastFormats[i].width * kSimulcastFormats[i].height) {
       return i;
     }
   }
   return -1;
 }
 
 int FindSimulcastFormatIndex(int width, int height, size_t max_layers) {
   MaybeExchangeWidthHeight(&width, &height);
 
   for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
-    if (width >= kSimulcastFormats[i].width &&
-        height >= kSimulcastFormats[i].height &&
+    if (width * height >=
+            kSimulcastFormats[i].width * kSimulcastFormats[i].height &&
         max_layers == kSimulcastFormats[i].max_layers) {
       return i;
     }
   }
   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);
   if (index == -1) {
     return -1;
   }
   return kSimulcastFormats[index].max_layers;
 }
 
 // TODO(marpan): Investigate if we should return 0 instead of -1 in
 // FindSimulcast[Max/Target/Min]Bitrate functions below, since the
 // codec struct max/min/targeBitrates are unsigned.
-int FindSimulcastMaxBitrateBps(int width, int height, size_t max_layers) {
+int FindSimulcastMaxBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
   if (format_index == -1) {
     return -1;
   }
   return kSimulcastFormats[format_index].max_bitrate_kbps * 1000;
 }
 
-int FindSimulcastTargetBitrateBps(int width,
-                                  int height,
-                                  size_t max_layers) {
+int FindSimulcastTargetBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
   if (format_index == -1) {
     return -1;
   }
   return kSimulcastFormats[format_index].target_bitrate_kbps * 1000;
 }
 
-int FindSimulcastMinBitrateBps(int width, int height, size_t max_layers) {
+int FindSimulcastMinBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
   if (format_index == -1) {
     return -1;
   }
   return kSimulcastFormats[format_index].min_bitrate_kbps * 1000;
 }
 
 bool SlotSimulcastMaxResolution(size_t max_layers, int* width, int* height) {
   int index = FindSimulcastFormatIndex(*width, *height, max_layers);
   if (index == -1) {
@@ skipping 10 matching lines @@
 
 int GetTotalMaxBitrateBps(const std::vector<webrtc::VideoStream>& streams) {
   int total_max_bitrate_bps = 0;
   for (size_t s = 0; s < streams.size() - 1; ++s) {
     total_max_bitrate_bps += streams[s].target_bitrate_bps;
   }
   total_max_bitrate_bps += streams.back().max_bitrate_bps;
   return total_max_bitrate_bps;
 }
 
-std::vector<webrtc::VideoStream> GetSimulcastConfig(
-    size_t max_streams,
-    int width,
-    int height,
-    int max_bitrate_bps,
-    int max_qp,
-    int max_framerate) {
-  size_t simulcast_layers = FindSimulcastMaxLayers(width, height);
-  if (simulcast_layers > max_streams) {
+std::vector<webrtc::VideoStream> GetSimulcastConfig(size_t max_streams,
+                                                    int width,
+                                                    int height,
+                                                    int max_bitrate_bps,
+                                                    int max_qp,
+                                                    int max_framerate,
+                                                    bool is_screencast) {
+  size_t num_simulcast_layers;
+  if (is_screencast) {
+    num_simulcast_layers =
+        UseSimulcastScreenshare() ? kDefaultScreenshareSimulcastStreams : 1;
+  } else {
+    num_simulcast_layers = FindSimulcastMaxLayers(width, height);
+  }
+
+  if (num_simulcast_layers > max_streams) {
     // If the number of SSRCs in the group differs from our target
     // number of simulcast streams for current resolution, switch down
     // to a resolution that matches our number of SSRCs.
     if (!SlotSimulcastMaxResolution(max_streams, &width, &height)) {
       return std::vector<webrtc::VideoStream>();
     }
-    simulcast_layers = max_streams;
+    num_simulcast_layers = max_streams;
   }
   std::vector<webrtc::VideoStream> streams;
-  streams.resize(simulcast_layers);
+  streams.resize(num_simulcast_layers);
 
-  // Format width and height has to be divisible by |2 ^ number_streams - 1|.
-  width = NormalizeSimulcastSize(width, simulcast_layers);
-  height = NormalizeSimulcastSize(height, simulcast_layers);
+  if (!is_screencast) {
+    // Format width and height has to be divisible by |2 ^ number_streams - 1|.
+    width = NormalizeSimulcastSize(width, num_simulcast_layers);
+    height = NormalizeSimulcastSize(height, num_simulcast_layers);
+  }
 
   // Add simulcast sub-streams from lower resolution to higher resolutions.
   // Add simulcast streams, from highest resolution (|s| = number_streams -1)
   // to lowest resolution at |s| = 0.
-  for (size_t s = simulcast_layers - 1;; --s) {
+  for (size_t s = num_simulcast_layers - 1;; --s) {
     streams[s].width = width;
     streams[s].height = height;
     // TODO(pbos): Fill actual temporal-layer bitrate thresholds.
-    streams[s].temporal_layer_thresholds_bps.resize(
-        kDefaultConferenceNumberOfTemporalLayers[s] - 1);
-    streams[s].max_bitrate_bps =
-        FindSimulcastMaxBitrateBps(width, height, simulcast_layers);
-    streams[s].target_bitrate_bps =
-        FindSimulcastTargetBitrateBps(width, height, simulcast_layers);
-    streams[s].min_bitrate_bps =
-        FindSimulcastMinBitrateBps(width, height, simulcast_layers);
     streams[s].max_qp = max_qp;
-    streams[s].max_framerate = max_framerate;
+    if (is_screencast && s == 0) {
+      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().
+      streams[s].min_bitrate_bps = kMinVideoBitrateKbps * 1000;
+      streams[s].target_bitrate_bps = config.tl0_bitrate_kbps * 1000;
+      streams[s].max_bitrate_bps = config.tl1_bitrate_kbps * 1000;
+      streams[s].temporal_layer_thresholds_bps.clear();
+      streams[s].temporal_layer_thresholds_bps.push_back(
+          config.tl0_bitrate_kbps * 1000);
+      streams[s].max_framerate = 5;
+    } else {
+      streams[s].temporal_layer_thresholds_bps.resize(
+          kDefaultConferenceNumberOfTemporalLayers[s] - 1);
+      streams[s].max_bitrate_bps = FindSimulcastMaxBitrateBps(width, height);
+      streams[s].target_bitrate_bps =
+          FindSimulcastTargetBitrateBps(width, height);
+      streams[s].min_bitrate_bps = FindSimulcastMinBitrateBps(width, height);
+      streams[s].max_framerate = max_framerate;
+    }
+
     width /= 2;
     height /= 2;
-    if (s == 0) {
+    if (s == 0)
       break;
-    }
   }
 
   // Spend additional bits to boost the max stream.
   int bitrate_left_bps = max_bitrate_bps - GetTotalMaxBitrateBps(streams);
   if (bitrate_left_bps > 0) {
     streams.back().max_bitrate_bps += bitrate_left_bps;
   }
 
   return streams;
 }
 
 static const int kScreenshareMinBitrateKbps = 50;
 static const int kScreenshareMaxBitrateKbps = 6000;
 static const int kScreenshareDefaultTl0BitrateKbps = 200;
 static const int kScreenshareDefaultTl1BitrateKbps = 1000;
 
 static const char* kScreencastLayerFieldTrialName =
     "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(kScreencastLayerFieldTrialName);
 
   ScreenshareLayerConfig config(kScreenshareDefaultTl0BitrateKbps,
@@ skipping 22 matching lines @@
       tl1_bitrate > kScreenshareMaxBitrateKbps || tl0_bitrate > tl1_bitrate) {
     return false;
   }
 
   config->tl0_bitrate_kbps = tl0_bitrate;
   config->tl1_bitrate_kbps = tl1_bitrate;
 
   return true;
 }
 
+bool UseSimulcastScreenshare() {
+  return webrtc::field_trial::FindFullName(
+             kSimulcastScreenshareFieldTrialName) == "Enabled";
+}
+
 }  // namespace cricket