We can add subtitles by using the track element. We can also use this element to feed metadata to scripts, create chapter titles, etc.; but more importantly, this element is used to provide more accessibility to the media and for improve Search Engine Optimisation.
<video controls
src="/media/cc0-videos/friday.mp4">
<track default
kind="captions"
srclang="en"
src="/media/examples/friday.vtt" />
Sorry, your browser doesn't support embedded videos.
</video>