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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.

Browser supported

Safari
Chrome
Opera
Firefox

List of program can open .vtt files

Product Name	Company	Actions
Atlantis Word Processor	The Atlantis Word Processor Team	open
GOM Player Plus	GOM & Company	Add to GOM Player Plus, open
PotPlayer	Kakao	Add to PotPlayer playlist, open, Play with PotPlayer
VisionTools Pro-e	Crestron Electronics, Inc	open

Good References

Technical Specs: https://www.w3.org/TR/webvtt1/
Metadata format can contain image, description, and its hyper link (href): https://www.w3.org/wiki/VTT_Concepts
WebVTT Example in HTML 5 implemented by Ian Devlin: https://www.iandevlin.com/html5test/webvtt/html5-video-webvtt-sample.html
Plugins supported: plyr.io, playr, Flowplayer, jwplayer, MediaElement.js, LeanBack Player, SublimeVideo, Video.js, Radiant Media Player. You can also have good information at https://videosws.praegnanz.de/ that shows HTML5 Video Player Comparison.