There are over a hundred legitimate subtitle file formats, each designed to support different types of applications and functional requirements. In this series of articles, we explain the main characteristics of each subtitle file format. This article provides further detail about the EBU-TT-D subtitle file format.

EBU-TT-D (EBU Timed Text – Distribution Format) is the European Broadcasting Union’s modern XML-based subtitle format designed for IP-based delivery workflows. It is widely adopted by public service and commercial broadcasters as the golden standard for delivering subtitles. Compared to legacy formats such as EBU STL, EBU-TT-D offers richer styling, responsive layout, Unicode support, and clean interoperability with web-native and OTT distribution pipelines.


For an overview of subtitle formats, see What is the Best Subtitle File Format?

TABLE OF CONTENTS

1. Introduction

EBU-TT-D is defined in EBU Tech 3380. It is based on the W3C Timed Text Markup Language (TTML1) and is optimised for the distribution of subtitle and caption data over IP networks, including streaming platforms and hybrid broadcast environments.


While EBU-TT (Tech 3350) is intended for production, interchange, and archiving, EBU-TT-D focuses specifically on delivery, offering predictable rendering, support for Unicode, responsive positioning, and compatibility with modern OTT workflows such as MPEG-DASH.


Public service and commercial broadcasters increasingly specify EBU-TT-D as their preferred delivery format due to its precision, flexibility, and long-term sustainability.


2. Key Characteristics of EBU-TT-D

According to the specification (Tech 3380) , EBU-TT-D is characterised by the following key characteristics.


XML-Based, Human-Readable Structure

EBU-TT-D files are well-formed XML documents using TTML vocabulary, with additional EBU-specific styling and metadata namespaces.


Precise Timing Based on Media Time

The format uses media time exclusively (ttp:timeBase="media") for accurate synchronisation with video and audio.


Responsive Layout and Styling

Lengths and coordinates are defined in percentages, enabling:

•    consistent rendering across device sizes

•    support for SD, HD, UHD, and mobile displays

•    adjustable regions, padding, and alignment


Unicode and Multi-Language Support

Documents use UTF-8 encoding, ensuring support for all scripts, including right-to-left (RTL) languages such as Arabic and Hebrew.


Strict Validation Rules

EBU-TT-D restricts TTML features for interoperability and predictable rendering (e.g., no pixel units, mandatory region definitions, no inline styling except under span).


Extensibility

Custom metadata is permitted through the tt:metadata element.


3. Structure of an EBU-TT-D File


The standardised structure of an EBU-TT-D document is described in Section 3 of Tech 3380 and consists of:


3.1 Root Element (tt:tt)


Contains:

  • language (xml:lang)
  • time base (ttp:timeBase="media")
  • optional attributes such as cellResolution


3.2 Head (tt:head)


Holds:

  • Metadata -— May include ttm:copyright or EBU metadata elements.
  • Styling(tt:styling) — Defines reusable styles using:
    • text colour (tts:color)
    • background colour (tts:backgroundColor)
    • font family and size
    • text alignment
    • ebutts:multiRowAlign (multi-row alignment)
    • ebutts:linePadding (padding for line backgrounds)
  • Layout(tt:layout) — Defines one or more tt:region elements specifying:
    • position (tts:origin)
    • size (tts:extent)
    • padding
    • background
    • writing mode (ltr, rtl, vertical)


3.3 Body (tt:body)


Container for subtitle content, containing:

  • tt:div — Organises subtitles into blocks.
  • tt:p — Represents an individual subtitle, with:
    • ID (xml:id)
    • timing (begin and end)
    • optional style and region attributes
  • tt:span — Inline styling within a subtitle for:
    • speaker labels
    • emphasis
    • colour changes
    • language changes
  • tt:br — Line breaks.


The full syntactic description is available in Annex B of https://tech.ebu.ch/publications/tech3380Tech 3380

 

4. Example EBU-TT-D File

The following simplified example illustrates the structure defined in the specification (e.g., Sections 3.1–3.2 of Tech 3380):


<tt xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xmlns:ebutts="urn:ebu:tt:style"
    ttp:timeBase="media"
    xml:lang="en">
 
  <head>
    <styling>
      <style xml:id="defaultStyle"
             tts:color="#FFFFFF"
             tts:fontFamily="Arial"
             tts:fontSize="5%"
             tts:textAlign="center"
      />
    </styling>
 
    <layout>
      <region xml:id="bottom"
              tts:origin="0% 80%"
              tts:extent="100% 20%"
              tts:displayAlign="after"
      />
    </layout>
  </head>
 
  <body style="defaultStyle">
    <div>
      <p xml:id="s1" begin="00:00:05.000" end="00:00:08.000" region="bottom">
        Welcome to the show!
      </p>
      <p xml:id="s2" begin="00:00:09.000" end="00:00:12.000" region="bottom">
        <span style="emphasis">Enjoy</span> the experience.
      </p>
    </div>
  </body>
</tt>


5. Features and Limitations

Features

✔ Rich Styling and Positioningm, supporting:

  • background boxes
  • multi-row alignment
  • line padding
  • placement by percentage (responsive)
  • vertical writing modes

✔ Unicode & Multi-Language Support: Structured to handle international scripts reliably.

✔ Broadcast-Grade Timing: Uses media timebase with precise begin/end values (Annex E) .

✔ Modern Delivery-Friendly: Designed for OTT, HbbTV, and DASH workflows.

✔ Future-Proof and Extensible: Flexible metadata framework (tt:metadata).

 

Limitations

✘ More Complex Than SRT or WebVTT: Its defined structure, namespaces, and constraints make it less accessible for manual authoring.

✘ Limited Inline Styling: Styling must reference declared tt:style elements, with controlled use of tt:span.

✘ No Pixel Units: By design, pixel-specific precision is not supported — only percentages and cell-based units — to ensure device-independent rendering. This may cause compatibility issues when converting back and forth other formats.


6. Limecraft Support for EBU-TT-D

Limecraft provides full support for EBU-TT-D as part of its professional subtitling and delivery workflows.


6.1 Import

  • Parses XML files including styling, regions, and timing.
  • Preserves formatting such as background colour, alignment, and line padding.
  • Validates structure according to EBU Tech 3380.


6.2 Export

  • Generates clean, fully compliant EBU-TT-D files.
  • Ensures correct:
    • region layout
    • timing precision
    • styling references
    • UTF-8 encoding
  • Supports broadcaster-specific delivery profiles (e.g., BBC requirements, via EBU-TT-D for BBC).


6.3 Use Cases

  • Conventional broadcast applications
  • OTT and VOD delivery
  • Regulatory accessibility compliance
  • Multilingual subtitling workflows


For related formats, see our articles on EBU STL, SRT, and DFXP/TTML.