timedtext

Timed text refers to text that is synchronized to media playback, such as captions, subtitles, and video description tracks. Each text cue has a start and end time, and the content can include styling and positioning information. Timed text is used to improve accessibility and understanding across broadcast, streaming, and online video.

The most prominent standards are TTML, the Timed Text Markup Language developed by the W3C, and WebVTT, a caption format designed for HTML5 video. TTML is an XML-based language that defines timing, structure, styling, and regions for on-screen text. Its earlier form, DFXP, contributed to TTML’s initial profiles, and TTML 2 expands capabilities for styling, layout, and internationalization. WebVTT is widely adopted for web video, offering a simpler, browser-friendly format that many platforms render directly.

In practice, TTML is common in professional workflows for broadcast and streaming, where caption files may be delivered as TTML or TTML-derived profiles. WebVTT is widely used on the web due to native browser support and straightforward integration with the track element in HTML5 video. Both formats support multiple language tracks, timing cues, and text formatting, and can be used for subtitling, closed captions, and accessibility descriptions.

Overall, timed text encompasses formats and standards that synchronize textual content with media. TTML and WebVTT represent two major implementations, each serving different delivery contexts while sharing the goal of making audiovisual media accessible to a broader audience.