start method
Implementation
Future<void> start(Function listener, Function onError,
{int sampleRate = 44000, int bufferSize = 5000}) async {
if (_audioCaptureEventChannelSubscription != null) return;
_audioCaptureEventChannelSubscription = _audioCaptureEventChannel
.receiveBroadcastStream({
"sampleRate": sampleRate,
"bufferSize": bufferSize
}).listen(listener, onError: onError);
}