onProgress
  onProgress property
A stream on which FlutterSound will post the recorder progression.
You may listen to this Stream to have feedback on the current recording. Don't forget to call also setSubscriptionDuration()!
Example
        _recorderSubscription = myRecorder.onProgress.listen((e)
        {
                Duration maxDuration = e.duration;
                double decibels = e.decibels
                ...
        }
        await myRecorder.setSubscriptionDuration(
            Duration(milliseconds: 100), // 100 ms
        );
See also
Implementation
Stream<RecordingDisposition>? get onProgress =>
    (_recorderController != null) ? _recorderController!.stream : null;