WebVTT made web captions a text file browsers could own

When video moved into HTML, subtitles could not stay as player-specific sidecars. WebVTT gave the web a caption file that looked like text, used millisecond cue timings, and fit directly into the browser media model.

The W3C draft defines WebVTT as the Web Video Text Tracks format for external text track resources connected to the HTML track element. MDN describes the format as plain text, UTF-8, with MIME type text/vtt and the .vtt extension.

The adoption move was pairing format and element. A video can reference multiple track files for captions, subtitles, chapters or metadata, and MDN marks both WebVTT and track as widely available across browsers since July 2015.

Make timed text native and readable

Plain text made captions easy to author, review and diff.

Native track support gave every video element a common place to attach timed text.

Cues covered captions first but also chapters and synchronized metadata.

CSS and JavaScript hooks let browsers standardize display without freezing every presentation choice.

A web format spreads when authors can edit it by hand, servers can serve it as text, and browsers can still turn it into a programmable native feature.

By mid-2015 WebVTT and the HTML track element were broadly available in browsers. The format became the default web caption sidecar for native audio and video, accessibility tooling and media metadata experiments.