WCAG: Enable VTT files to be created for videos

[What is a VTT file?](https://www.simultrans.com/blog/what-is-a-vtt-file)
[Web Video Text Tracks Format (WebVTT)](https://developer.mozilla.org/en-US/docs/Web/API/WebVTT_API/Web_Video_Text_Tracks_Format)
[WCAG Video caption](https://dequeuniversity.com/rules/axe/4.10/video-caption)

Can possibly be generated automatically by AI.