This specification defines WebVTT, the Web Video Text Tracks format. Its main use is for marking up external text track resources in connection with the HTML <track> element. WebVTT files provide captions or subtitles for video content, and also text video descriptions, chapters for content navigation, and more generally any form of metadata that is time-aligned with audio or video content.
Technical Specs: https://www.w3.org/TR/webvtt1/
WebVTT Example in HTML 5 implemented by Ian Devlin: https://www.iandevlin.com/html5test/webvtt/html5-video-webvtt-sample.html