Dynacast (#62)

* signal

* engine

* dynacast option

* implement

* update for non simulcast

* use low when rid is null

* firefox comment

lib/src/publication/local.dart

@@ -1,5 +1,11 @@
+import 'package:collection/collection.dart';
+import 'package:meta/meta.dart';
+
+import '../extensions.dart';
+import '../logger.dart';
 import '../participant/local.dart';
 import '../proto/livekit_models.pb.dart' as lk_models;
+import '../proto/livekit_rtc.pb.dart' as lk_rtc;
 import '../track/local/local.dart';
 import 'track_publication.dart';
 
@@ -27,4 +33,40 @@ class LocalTrackPublication<T extends LocalTrack> extends TrackPublication<T> {
 
   /// Unmute the track associated with this publication
   Future<void> unmute() async => await track?.unmute();
+
+  @internal
+  void updatePublishingLayers(List<lk_rtc.SubscribedQuality> layers) async {
+    //
+    final params = track?.sender?.parameters;
+    if (params == null) return;
+
+    final encodings = params.encodings;
+    if (encodings == null) return;
+
+    bool didChange = false;
+
+    for (final encoding in encodings) {
+      final layer = layers.firstWhereOrNull((e) =>
+          // If there is exact match, use it
+          (e.quality.toRid() == encoding.rid) ||
+          // Use low layer if rid is null (not simulcast)
+          (encoding.rid == null && e.quality == lk_models.VideoQuality.LOW));
+      if (layer != null && encoding.active != layer.enabled) {
+        encoding.active = layer.enabled;
+        logger.fine('Setting layer ${layer.quality} to ${layer.enabled}');
+        // FireFox does not support setting encoding.active to false, so we
+        // have a workaround of lowering its bitrate and resolution to the min.
+        // TODO: Workaround for firefox
+        didChange = true;
+      }
+    }
+
+    if (didChange) {
+      params.encodings = encodings;
+      final result = await track?.sender?.setParameters(params);
+      if (result == false) {
+        logger.warning('Failed to update sender parameters');
+      }
+    }
+  }
 }