Add support for configuring the number of spatial/temporal layers for VP9 through a field trial.

webrtc/media/engine/webrtcvideoengine2.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 "webrtc/media/engine/webrtcvideoengine2.h"
 
+#include <stdio.h>
 #include <algorithm>
 #include <set>
 #include <string>
 
 #include "webrtc/base/buffer.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/stringutils.h"
 #include "webrtc/base/timeutils.h"
 #include "webrtc/base/trace_event.h"
 #include "webrtc/call.h"
@@ skipping 285 matching lines @@
     return 600;
   } else if (width * height <= 640 * 480) {
     return 1700;
   } else if (width * height <= 960 * 540) {
     return 2000;
   } else {
     return 2500;
   }
 }
 
+bool GetVp9LayersFromFieldTrialGroup(int* num_spatial_layers,
+                                     int* num_temporal_layers) {
+  std::string group = webrtc::field_trial::FindFullName("WebRTC-SupportVP9SVC");
+  if (group.empty())
+    return false;
+
+  if (sscanf(group.c_str(), "EnabledByFlag_%dSL%dTL", num_spatial_layers,
+             num_temporal_layers) != 2) {
+    return false;
+  }
+  const int kMaxSpatialLayers = 3;
+  if (*num_spatial_layers > kMaxSpatialLayers || *num_spatial_layers < 1)
+    return false;
+
+  const int kMaxTemporalLayers = 3;
+  if (*num_temporal_layers > kMaxTemporalLayers || *num_temporal_layers < 1)
+    return false;
+
+  return true;
+}
+
+int GetDefaultVp9SpatialLayers() {
+  int num_sl;
+  int num_tl;
+  if (GetVp9LayersFromFieldTrialGroup(&num_sl, &num_tl)) {
+    return num_sl;
+  }
+  return 1;
+}
+
+int GetDefaultVp9TemporalLayers() {
+  int num_sl;
+  int num_tl;
+  if (GetVp9LayersFromFieldTrialGroup(&num_sl, &num_tl)) {
+    return num_tl;
+  }
+  return 1;
+}
 }  // namespace
 
 // Constants defined in webrtc/media/engine/constants.h
 // TODO(pbos): Move these to a separate constants.cc file.
 const int kMinVideoBitrate = 30;
 const int kStartVideoBitrate = 300;
 
 const int kVideoMtu = 1200;
 const int kVideoRtpBufferSize = 65536;
 
@@ skipping 108 matching lines @@
     encoder_settings_.vp8 = webrtc::VideoEncoder::GetDefaultVp8Settings();
     encoder_settings_.vp8.automaticResizeOn = automatic_resize;
     // VP8 denoising is enabled by default.
     encoder_settings_.vp8.denoisingOn =
         codec_default_denoising ? true : denoising;
     encoder_settings_.vp8.frameDroppingOn = frame_dropping;
     return &encoder_settings_.vp8;
   }
   if (CodecNamesEq(codec.name, kVp9CodecName)) {
     encoder_settings_.vp9 = webrtc::VideoEncoder::GetDefaultVp9Settings();
+    encoder_settings_.vp9.numberOfSpatialLayers = GetDefaultVp9SpatialLayers();

[pbos-webrtc, 2016/03/17 14:34:38]

I don't think this should apply to screenshare, should it? Otherwise these
DCHECKs should probably be removed as well:

https://chromium.googlesource.com/external/webrtc/+/b4c82474be64b815141284e37...

[åsapersson, 2016/03/17 16:57:34]

Ok, changed so it is not set for screenshare for now. Also, set spatial layers
to 2 if screenshare and added a comment/todo.

     // VP9 denoising is disabled by default.
     encoder_settings_.vp9.denoisingOn =
         codec_default_denoising ? false : denoising;
     encoder_settings_.vp9.frameDroppingOn = frame_dropping;
     return &encoder_settings_.vp9;
   }
   return NULL;
 }
 
 DefaultUnsignalledSsrcHandler::DefaultUnsignalledSsrcHandler()
@@ skipping 1407 matching lines @@
     // For 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().
     encoder_config.streams[0].target_bitrate_bps =
         config.tl0_bitrate_kbps * 1000;
     encoder_config.streams[0].max_bitrate_bps = config.tl1_bitrate_kbps * 1000;
     encoder_config.streams[0].temporal_layer_thresholds_bps.clear();
     encoder_config.streams[0].temporal_layer_thresholds_bps.push_back(
         config.tl0_bitrate_kbps * 1000);
   }
+  if (CodecNamesEq(codec.name, kVp9CodecName) &&
+      encoder_config.streams.size() == 1) {
+    encoder_config.streams[0].temporal_layer_thresholds_bps.resize(
+        GetDefaultVp9TemporalLayers() - 1);
+  }
   return encoder_config;
 }
 
 void WebRtcVideoChannel2::WebRtcVideoSendStream::SetDimensions(
     int width,
     int height) {
   if (last_dimensions_.width == width && last_dimensions_.height == height &&
       !pending_encoder_reconfiguration_) {
     // Configured using the same parameters, do not reconfigure.
     return;
@@ skipping 648 matching lines @@
         rtx_mapping[video_codecs[i].codec.id] !=
             fec_settings.red_payload_type) {
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket