.TTML

Introduction

TTML, the Timed Text Markup Language, is an XML format for subtitles and captions specified by the W3C. It is used mainly by broadcasters and streaming services, where subtitles are delivered to many kinds of player. Profiles of TTML include IMSC, used in MPEG-DASH and CMAF streams, SMPTE-TT and the EBU’s EBU-TT.

The first version of TTML was originally called DFXP, the Distribution Format Exchange Profile, and files with the .dfxp extension are TTML. Some services also deliver TTML as .xml files.

Structure

The root element is tt in the namespace http://www.w3.org/ns/ttml, with an xml:lang attribute. The optional head holds styling, with named styles using attributes such as tts:color and tts:fontStyle, and layout, with the regions of the screen where text can appear. The body holds div elements of p paragraphs, each with begin and end times; br breaks a line and span styles part of it.

<tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="en">
  <body>
    <div>
      <p begin="00:00:01.000" end="00:00:03.500">Where are we going?</p>
      <p begin="00:00:04.000" end="00:00:06.250"><span tts:fontStyle="italic">Somewhere we have never been.</span></p>
    </div>
  </body>
</tt>

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