Timed Text Markup Language (TTML)

What is a TTML file?

TTML (Timed Text Markup Language) is the W3C’s XML standard for captions and subtitles. TTML1 became a W3C Recommendation in 2010, and TTML2 followed in 2018. TTML is less a single file format than a family: SMPTE-TT, IMSC, EBU-TT, DFXP, Apple’s iTT and the Netflix timed text profiles are all built on it.

A TTML document has a <tt> root, a <head> that defines styles and layout regions, and a <body> of <div>, <p> and <span> elements with begin, end or dur timing. Times can be clock values (00:00:01.500), frames (00:00:01:12 with a declared ttp:frameRate), or ticks against a ttp:tickRate. Styles cover font, color, background, alignment and more. Regions place text anywhere on screen with tts:origin and tts:extent.

That flexibility is TTML’s strength and its main pitfall. Two valid TTML files can use completely different timing, styling and layout conventions, and most delivery specifications only accept a tightly constrained profile. Choosing the right target profile matters as much as the conversion itself.

<?xml version="1.0" encoding="UTF-8"?>
<tt xmlns="http://www.w3.org/ns/ttml"
    xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="en">
  <head>
    <styling>
      <style xml:id="s1" tts:color="white" tts:textAlign="center"/>
    </styling>
    <layout>
      <region xml:id="bottom" tts:origin="10% 80%" tts:extent="80% 15%"/>
    </layout>
  </head>
  <body style="s1" region="bottom">
    <div>
      <p begin="00:00:01.000" end="00:00:03.500">Where were you last night?</p>
    </div>
  </body>
</tt>

TTML profiles in Closed Caption Converter

Besides the base TTML profile, Closed Caption Converter reads and writes delivery-specific TTML variants. These include DFXP, SMPTE TTML, IMSC 1.0 Basic, IMSC Text Captions and Subtitles, EBU-TT, iTT, Netflix DFXP and Netflix TT, Sandflow TTML, YouTube TTML and several encode-only broadcaster profiles. When you are delivering to a platform, choose the profile named for it rather than generic TTML.