What is TTML / DFXP format?
TTML (Timed Text Markup Language) is an XML-based subtitle format used in broadcast and streaming. DFXP (Distribution Format Exchange Profile) is an older TTML profile. Both are interchangeable in most workflows — convert to SRT for editing.
Detail
TTML (Timed Text Markup Language) is a W3C standard for timed text, encoded in XML. It was designed for professional broadcast and streaming workflows where rich styling metadata (fonts, positions, colors, regions) needs to travel alongside the text. DFXP (Distribution Format Exchange Profile) is an older TTML profile used by Amazon, Hulu, and early streaming platforms — it's effectively TTML under a different name. Both look like XML files with <tt>, <body>, <div>, and <p> elements. In practice, most video editors and consumer tools don't read TTML/DFXP natively — you'll encounter these formats when receiving deliverables from broadcast partners or streaming platforms, and the typical workflow is to convert to SRT for editing, then re-convert to TTML for final delivery. The SoCaptions SRT-to-TTML and TTML-to-SRT converters handle both directions.
SRT for almost everything: video editors, YouTube, Vimeo, every major platform. VTT only when you're embedding video on a website with HTML5 <track>.
SRT (SubRip Subtitle) is a plain-text subtitle format with numbered cues and HH:MM:SS,mmm timestamps. It's the most universal subtitle format.