XML format

TTML captions

Timed text for subtitles and captions, carrying styling and positioning that SRT cannot — and the profile that broadcasters require.

TTML is the XML format behind broadcast and streaming captions, and the reason to reach for it over SRT is everything SRT cannot say: positioning, colour, region, alignment and the styling rules that make a caption legible over a bright shot. Its structure is deliberately CSS-like — styles are declared in <head> and referenced by id, not repeated inline.

The catch is that TTML is a family of profiles rather than one format. IMSC is what streaming platforms require, EBU-TT-D is what European broadcasters require, and SMPTE-TT is another. A document valid against the base TTML schema can be rejected by all three, because each profile constrains it further.

Constraints that bite

Times are expressed in whichever form the document declares — clock time, offset, or frames — and reading them without checking ttp:timeBase and ttp:frameRate gives the wrong answer.
Profiles matter more than the base schema. IMSC, EBU-TT-D and SMPTE-TT each narrow TTML, and platforms validate against the profile.
Regions and styles are referenced by id from <head>; an unresolved reference renders without styling rather than failing.
xml:lang on the root is required in most profiles and is how a player labels the caption track.
A caption that overlaps another in the same region is legal XML and a rendering defect; overlap has to be checked separately.

Root element: <tt>
Media type: application/ttml+xml
Extensions: .ttml, .dfxp, .xml
Namespaces: http://www.w3.org/ns/ttml
XMLDir label: —

Specification: W3C TTML2

A minimal valid document

Every example on this site is checked against the same parser the workspace uses, so what you see below is known to be well-formed.

ttml.xml

<?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="base" tts:color="white" tts:backgroundColor="black"
             tts:fontSize="80%" tts:textAlign="center"/>
    </styling>
    <layout>
      <region xml:id="bottom" tts:origin="10% 80%" tts:extent="80% 15%"/>
    </layout>
  </head>
  <body region="bottom">
    <div>
      <p begin="00:00:01.000" end="00:00:04.000" style="base">The engine weaves algebraic patterns.</p>
      <p begin="00:00:04.500" end="00:00:07.000" style="base">As the loom weaves flowers.</p>
    </div>
  </body>
</tt>

Validate your own TTML captions Extract its XPath map