Dynamic progress vis

Hello,

Awesome component, thank you so much!

To visualize the progress of the playback dynamically I've used this:
```
onTimeUpdate(e) {
    this.waveform.overlayEl.nativeElement.style.width = e.progress + '%';
}
```
...which works fine, but it feels a bit hacky. Is there some intended way to get a playhead or to update the progress dynamically?
