Reference

TTML

TTML (Timed Text Markup Language) is an XML-based format for captions and subtitles, used in broadcast and streaming. It pairs timed text with styling and layout, and underlies profiles like SMPTE-TT and the IMSC captions used by streaming services.

Files & formatsGeneral

TTML

Also known as: .ttml file, Timed Text Markup Language, DFXP, timed text

XML-based caption and subtitle format
Used in broadcast and streaming (DFXP, SMPTE-TT, IMSC)
More capable but more verbose than SRT/VTT

What TTML is for

TTML is a W3C standard that stores captions as XML: each subtitle is an element with timing, text, and optional styling and positioning. It is designed for professional broadcast and streaming workflows rather than casual file sharing.

You will see it behind the scenes in streaming captions and broadcast subtitling, sometimes under names like DFXP, SMPTE-TT, or IMSC, which are TTML profiles tuned for specific industries.

TTML vs SRT and VTT

Compared with SRT or WebVTT, TTML is more verbose and more capable: it carries layout and styling that simpler formats lack, at the cost of being harder to read and edit by hand.

It is a small plain-text (XML) file, so storage is never a concern. For everyday video and web captions, VTT is more common; TTML shows up mainly in professional and broadcast pipelines.

Related terms

Keep reading the reference.

Files & formatsSRT (SubRip subtitles)An SRT file is a plain-text subtitle file in the SubRip format. It lists numbered captions, each with a start and end timecode and the line of text to show, so a player can overlay subtitles on a video. Because it is just text, an SRT file is tiny — usually a few kilobytes.General Files & formatsWebVTT (.vtt subtitles)A VTT (WebVTT) file is a plain-text caption and subtitle format built for web video, used by the HTML5 video player. Like SRT it stores timecoded text, but it adds styling, positioning, and metadata. It is a small text file, typically only a few kilobytes.General Files & formatsASS / SSA subtitlesASS (Advanced SubStation Alpha) and its predecessor SSA are subtitle formats that add styling on top of plain text — fonts, colors, positioning, and on-screen effects. Unlike a basic SRT, an .ass file can place and animate captions anywhere on screen, which is why fansubs and anime use it.General Files & formatsXMLXML (Extensible Markup Language) is a text-based format that stores structured data inside nested, custom-named tags, such as `<title>…</title>`. It is self-describing and widely used for documents, configuration, RSS feeds, and data exchange between systems.General