set the simulcast codec & layers (#891)

Author: chenosaurus

livekit/src/room/participant/local_participant.rs

@@ -284,6 +284,16 @@ impl LocalParticipant {
 
                 encodings = compute_video_encodings(req.width, req.height, &options);
                 req.layers = video_layers_from_encodings(req.width, req.height, &encodings);
+
+                // Populate simulcast_codecs so the server knows this track is simulcasted
+                if options.simulcast && encodings.len() > 1 {
+                    req.simulcast_codecs = vec![proto::SimulcastCodec {
+                        codec: options.video_codec.as_str().to_string(),
+                        cid: track.rtc_track().id(),
+                        layers: req.layers.clone(),
+                        ..Default::default()
+                    }];
+                }
             }
             LocalTrack::Audio(_audio_track) => {
                 // Setup audio encoding