WebVTT: Web Video Text Tracks is a concerted effort to bring subtitles that run natively on the browser to the web. WebVTT functions by attaching an external WebVTT file to the <video> element via the <track> element like so:
<video src="video.webm"> <track src="sample.vtt"> </video>
Where sample.vtt is an external WebVTT file marked up like so:
WEBVTT 00:01.000 --> 00:03.000 Hey! 00:03.000 --> 00:05.000 This is a sample!
Currently you can view basic subtitles in Mozilla's Nightly builds. The basic WebVTT tags such as <b>, <u>, and <i> are working.
To try it out, enter about:config in the address bar and set the media.webvtt.enabled pref to true. Then visit a demo page like this one.