checkAudioTracksChanged_(from, to) {
    let dispatchEvent = false;
    if (!from || from.audioId != to.audioId ||
        from.audioGroupId != to.audioGroupId) {
      dispatchEvent = true;
    }
    if (dispatchEvent) {
      this.onAudioTracksChanged_();
    }
  }
Dispatches a 'audiotrackschanged' event if necessary
@param {?shaka.extern.Track} from
@param {shaka.extern.Track} to
@private