setPlaybackRate method

Implementation

@override
  void setPlaybackRate(double value){
	if (!hasPlaybackControl) {
		console.warning( 'Audio: this Audio has no playback control.' );
		return;
	}

	if (isPlaying) {
      playbackRate = value;
		source == null?null:SoLoud.instance.setRelativePlaySpeed(source!,value);
	}
}