VTT Format (WebVTT)

Definition

VTT, which stands for Web Video Text Tracks, is a plain-text subtitle and caption file format defined by the World Wide Web Consortium (W3C) as the standard for the HTML5 <track> element. Files use the .vtt extension and are the native subtitle format for web-based video players including browsers like Chrome, Firefox, Safari, and Edge, as well as platforms built on HTML5 video. A VTT file begins with the mandatory header line 'WEBVTT' followed by an optional file description block, then a series of caption cues. Each cue consists of an optional cue identifier, a timecode range (formatted as HH:MM:SS.mmm --> HH:MM:SS.mmm, using a period rather than the comma used in SRT), and the caption text. VTT supports additional cue settings after the timecode that control text positioning, alignment, and line placement — capabilities that SRT lacks. Beyond basic captions, VTT supports several extended features: cue positioning and alignment settings allow precise placement of text anywhere in the video frame; region definitions allow text to be constrained to a defined area; voice spans (using <v Speaker Name> tags) can attribute dialogue to named speakers; and chapter markers can be defined in separate VTT files for video navigation. CSS styling can also be applied to VTT captions in supported browsers through the ::cue pseudo-element. For streaming platforms and CDN-delivered video, VTT is frequently used alongside HLS and MPEG-DASH streams because adaptive bitrate players commonly use VTT tracks for subtitle delivery. For accessibility compliance on the web, VTT is the recommended format for closed captions delivered via the <track> element. While VTT is the technical standard for web video, SRT remains more universally supported across social platforms, desktop media players, and video editing software. In practice, many workflows generate one format and convert it to the other as needed — the two formats are structurally very similar and conversion is straightforward.