feature: switch between front and back cameras

lib/src/track/local_video_track.dart

@@ -5,6 +5,8 @@ import 'options.dart';
 import 'video_track.dart';
 
 class LocalVideoTrack extends VideoTrack {
+  RTCRtpSender? get sender => transceiver?.sender;
+
   LocalVideoTrack(String name, MediaStreamTrack mediaTrack, MediaStream stream)
       : super(name, mediaTrack, stream);
 
@@ -14,6 +16,41 @@ class LocalVideoTrack extends VideoTrack {
       options = LocalVideoTrackOptions(params: VideoPresets.qhd);
     }
 
+    try {
+      var stream = await _createCameraStream(options);
+      return LocalVideoTrack("camera", stream.getVideoTracks().first, stream);
+    } catch (e) {
+      return Future.error(e);
+    }
+  }
+
+  Future<void> restartTrack([LocalVideoTrackOptions? options]) async {
+    if (sender == null) {
+      return Future.error(TrackCreateError('could not restart track'));
+    }
+
+    if (options == null) {
+      options = LocalVideoTrackOptions(params: VideoPresets.qhd);
+    }
+
+    try {
+      var stream = await _createCameraStream(options);
+      var track = stream.getVideoTracks().first;
+      mediaStream = stream;
+      await mediaTrack.stop();
+      mediaTrack = track;
+      await sender?.replaceTrack(track);
+    } catch (e) {
+      return Future.error(e);
+    }
+  }
+
+  static Future<MediaStream> _createCameraStream(
+      LocalVideoTrackOptions? options) async {
+    if (options == null) {
+      options = LocalVideoTrackOptions(params: VideoPresets.qhd);
+    }
+
     try {
       var stream = await navigator.mediaDevices.getUserMedia({
         "audio": false,
@@ -24,7 +61,7 @@ class LocalVideoTrack extends VideoTrack {
         return Future.error(TrackCreateError());
       }
 
-      return LocalVideoTrack("camera", stream.getVideoTracks().first, stream);
+      return stream;
     } catch (e) {
       return Future.error(e);
     }