setPlaybackRate method
Sets the playback rate - call this after first calling play() or resume().
iOS and macOS have limits between 0.5 and 2x Android SDK version should be 23 or higher. not sure if that's changed recently.
Implementation
Future<int> setPlaybackRate({double playbackRate = 1.0}) {
return _invokeMethod('setPlaybackRate', {'playbackRate': playbackRate});
}