WebVTT is the caption format <track> loads (Multimedia): a WEBVTT header, then cues such as 01:10.000 --> 01:14.000 line:0 followed by text with <b>, <i> or <v Speaker> tags. Style them with video::cue. Script them too: video.addTextTrack('captions') returns a track, track.addCue(new VTTCue(70, 74, 'So beat it')) adds a cue, and cuechange with track.activeCues lets you sync a transcript or draw custom captions (track.mode = 'hidden' keeps events but hides native rendering). OpenAI 86 's MIT-licensed Whisper 109,655 (https://github.com/openai/whisper 109,655 ) writes captions with whisper talk.mp4 --output_format vtt.