start method
Implementation
void start({bool resolveImages = false, NowPlayingImageResolver resolver}) async { // async, but should not be awaited
this._resolveImages = resolver != null || resolveImages;
this._resolver = resolver ?? _NowPlayingImageResolver();
_controller = StreamController<NowPlayingTrack>.broadcast();
_controller.add(NowPlayingTrack.notPlaying);
await _bindToWidgetsBinding();
if (Platform.isAndroid) _channel.setMethodCallHandler(_handler);
if (Platform.isIOS) _refreshTimer = Timer.periodic(_refreshPeriod, _refresh);
_refresh();
}