Feature: Enable a mechanism to show/hide captions on-demand

Currently, there is a possibility to autoplay a muted video with a captions track shown. However, there is no way to, for instance, hide those captions if user disables `muted`.

Since the video is behind and iframe, there is no way to access to the `tracks` and hide them using something like

```js
videoRef.textTracks[0].mode = 'hidden'
```