Make video scalability mode configurable from peerconnection level.

This CL does not aim at cleaning up simulcast/SVC configuration, just to make it possible to set the scalability mode for AV1. Implementing a codec agnostic SVC/simulcast API is a (big) project on its own.

Change-Id: Ia88df31eb1111713e5f8832e95c8db44f92887ca

BUG: webrtc:11607
Change-Id: Ia88df31eb1111713e5f8832e95c8db44f92887ca
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/192541
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32631}

api/rtp_parameters.h

@@ -465,6 +465,9 @@ struct RTC_EXPORT RtpEncodingParameters {
   // For video, scale the resolution down by this factor.
   absl::optional<double> scale_resolution_down_by;
 
+  // https://w3c.github.io/webrtc-svc/#rtcrtpencodingparameters
+  absl::optional<std::string> scalability_mode;
+
   // For an RtpSender, set to true to cause this encoding to be encoded and
   // sent, and false for it not to be encoded and sent. This allows control
   // across multiple encodings of a sender for turning simulcast layers on and

api/video_codecs/video_encoder_config.h

@@ -64,6 +64,8 @@ struct VideoStream {
   // between multiple streams.
   absl::optional<double> bitrate_priority;
 
+  absl::optional<std::string> scalability_mode;
+
   // If this stream is enabled by the user, or not.
   bool active;
 };

media/engine/webrtc_video_engine.cc

@@ -2261,9 +2261,11 @@ webrtc::RTCError WebRtcVideoChannel::WebRtcVideoSendStream::SetRtpParameters(
   // TODO(bugs.webrtc.org/8807): The bitrate priority really doesn't require an
   // entire encoder reconfiguration, it just needs to update the bitrate
   // allocator.
-  bool reconfigure_encoder =
-      new_param || (new_parameters.encodings[0].bitrate_priority !=
-                    rtp_parameters_.encodings[0].bitrate_priority);
+  bool reconfigure_encoder = new_param ||
+                             (new_parameters.encodings[0].bitrate_priority !=
+                              rtp_parameters_.encodings[0].bitrate_priority) ||
+                             new_parameters.encodings[0].scalability_mode !=
+                                 rtp_parameters_.encodings[0].scalability_mode;
 
   // TODO(bugs.webrtc.org/8807): The active field as well should not require
   // a full encoder reconfiguration, but it needs to update both the bitrate
@@ -2422,6 +2424,8 @@ WebRtcVideoChannel::WebRtcVideoSendStream::CreateVideoEncoderConfig(
   for (size_t i = 0; i < encoder_config.simulcast_layers.size(); ++i) {
     encoder_config.simulcast_layers[i].active =
         rtp_parameters_.encodings[i].active;
+    encoder_config.simulcast_layers[i].scalability_mode =
+        rtp_parameters_.encodings[i].scalability_mode;
     if (rtp_parameters_.encodings[i].min_bitrate_bps) {
       encoder_config.simulcast_layers[i].min_bitrate_bps =
           *rtp_parameters_.encodings[i].min_bitrate_bps;

modules/video_coding/video_codec_initializer.cc

@@ -94,6 +94,7 @@ VideoCodec VideoCodecInitializer::VideoEncoderConfigToVideoCodec(
 
   int max_framerate = 0;
 
+  absl::optional<std::string> scalability_mode = streams[0].scalability_mode;
   for (size_t i = 0; i < streams.size(); ++i) {
     SpatialLayer* sim_stream = &video_codec.simulcastStream[i];
     RTC_DCHECK_GT(streams[i].width, 0);
@@ -126,6 +127,15 @@ VideoCodec VideoCodecInitializer::VideoEncoderConfigToVideoCodec(
     video_codec.qpMax = std::max(video_codec.qpMax,
                                  static_cast<unsigned int>(streams[i].max_qp));
     max_framerate = std::max(max_framerate, streams[i].max_framerate);
+
+    if (streams[0].scalability_mode != streams[i].scalability_mode) {
+      RTC_LOG(LS_WARNING) << "Inconsistent scalability modes configured.";
+      scalability_mode.reset();
+    }
+  }
+
+  if (scalability_mode.has_value()) {
+    video_codec.SetScalabilityMode(*scalability_mode);
   }
 
   if (video_codec.maxBitrate == 0) {

video/video_stream_encoder.cc

@@ -149,6 +149,11 @@ bool RequiresEncoderReset(const VideoCodec& prev_send_codec,
       }
     }
   }
+
+  if (new_send_codec.ScalabilityMode() != prev_send_codec.ScalabilityMode()) {
+    return true;
+  }
+
   return false;
 }