Stream State Update (#53)

* implemented

* update docs

lib/src/publication/remote_track_publication.dart

@@ -13,6 +13,7 @@ import '../participant/remote_participant.dart';
 import '../proto/livekit_models.pb.dart' as lk_models;
 import '../proto/livekit_rtc.pb.dart' as lk_rtc;
 import '../track/remote.dart';
+import '../types.dart';
 import '../utils.dart';
 import 'track_publication.dart';
 
@@ -40,6 +41,27 @@ class RemoteTrackPublication<T extends RemoteTrack>
   lk_models.VideoQuality _videoQuality = lk_models.VideoQuality.HIGH;
   lk_models.VideoQuality get videoQuality => _videoQuality;
 
+  StreamState _streamState = StreamState.paused;
+
+  /// The server may pause the track when they are bandwidth limitations and resume
+  /// when there is more capacity. This property will be updated when the track is
+  /// paused / resumed by the server. See [TrackStreamStateUpdatedEvent] for the
+  /// relevant event.
+  StreamState get streamState => _streamState;
+
+  @internal
+  Future<void> updateStreamState(StreamState streamState) async {
+    // return if no change
+    if (_streamState == streamState) return;
+    _streamState = streamState;
+    [participant.events, participant.room.events]
+        .emit(TrackStreamStateUpdatedEvent(
+      participant: participant,
+      trackPublication: this,
+      streamState: streamState,
+    ));
+  }
+
   // used to report renderer visibility to the server
   // and optimize
   final _visibilities = <String, RendererVisibility>{};