Media Access Technology

Helps Members make audiovisual media accessible by contributing technology, production standards, and guidance.

Broadcasters and online service providers are increasingly looking to use subtitles, audio description, sign interpretation and other adaptations to help make their content more accessible. Accessibility services also add perceived value and deliver additional benefits such as opportunities for personalisation. At the same time, the operation of accessibility services is greatly facilitated by technology advances such as IP-based production and machine learning technology. This group aims to address common issues to help with the production, exchange, archiving, distribution and playback of accessible audio-visual media.

Currently the following deliverables are planned (green indicates the deliverable has already been delivered). Note that deliverables are dependent on enough participation in the work, and that the planning is subject to change. New deliverables are added regularly.


  • status_med_12px.png Subtitling Challenges of Today
  • status_med_12px.png Addition of QC Tests on Subtitling
  • status_med_12px.png Update of Tech-3381
  • status_med_12px.png Tech Review: Audio Description Dip Levels for Non-Sound Engineers  







Technical aspects of accessibility technology for media are being addressed by the EBU Media Access Technology group, which is part of the EBU's Strategic Programme on Production.

Main activities:

  • Help Members to use subtitles in new file-based facilities and for new distribution platforms.
  • Develop broadcast specifications based on the W3C Timed Text Markup Language (TTML).
  • Provide mappings and example files to help you use the format for subtitling.


To meet broadcasers' requirements, the EBU Media Access Technology Group has created EBU-TT, which stands for EBU Timed Text. EBU-TT is the follow-up to the widely used EBU STL format (EBU Tech 3264). The EBU-TT family consists of the following specifications:

EBU-TT Part 1: Archive & Exchange

EBU-TT Part 1 (EBU Tech 3350) defines an easy-to-use XML structure for the interchange and archiving of subtitles. It builds on the W3C Timed text Markup Language (TTML) 1.0.

EBU-TT Part 2: STL mapping

EBU-TT Part 2 (EBU Tech 3360) is a mapping guide on how to map EBU STL files to EBU-TT.


Since May 2017, the EBU-TT metadata elements are defined in a single document (EBU Tech 3390). This makes it easier to maintain an overview and avoid duplication.

EBU-TT Part 3: Live contribution

EBU-TT Part 3 (EBU Tech 3370) provides a System Model and Content Profile for authoring and contribution of live (and prepared) subtitling. It further introduces the concept of processing 'nodes' that can help improve subtitling quality in production. This part is also known as "EBU-TT Live".

EBU-TT WebSocket Carriage Specification

EBU-TT Live does not prescribe which carrier mechanisms to use. These mechanisms can be defined in supplemental publications. EBU Tech 3370s1 is such a supplement. It describes how to carry EBU-TT-Live streams using WebSocket.

EBU-TT Live Interoperability Toolkit

This is not an official EBU spec, but an Open Source project that builds on the EBU-TT Live spec. It was used to test the specification in code and is a useful resource when adding EBU-TT Live support to products. See for more.


EBU-TT part 'D' (EBU Tech 3380) is the format for the distribution of subtitles over IP. There also is a document for the use of EBU-TT-D in ISO BMFF /  MPEG-DASH (EBU Tech 3381). Other specs reference EBU-TT-D, such as HbbTV 2.0, DVB TTML Subtitling and Freeview Play. 

Related publications

The EBU has also developed a recommendation on the transport of subtitles inside and outside of MXF files (EBU R 133).

EBU Member BBC has published BBC Subtitles Guidelines. These are intended to serve as the basis for all subtitle work across the BBC (prepared and live, online and broadcast, internal and supplied)

Quality Control Tests

The EBU Quality Control Group is extending the range of QC Tests for subtitling. All published tests are available via EBU.IO/QC. To participate in the drafting work, join the QC group.


Also check out this list of existing open source subtitling software and samples.

We are aware of the following parties supporting EBU-TT and/or IMSC in products/tools.*

EBU-TT Part 1

EZtitles - Subtitling software that can be purchased or rented.

Subtitling Conversion Framework (SCF) - A set of open source modules for converting subtitle formats.

EBU-TT Part 2

Subtitling Conversion Framework (SCF) - A set of open source modules for converting subtitle formats.

Subito - Captioning platform from Red Bee

EBU-TT-Live (part 3)

EBU-TT Live Interoperability Toolkit - A set of components for generating, testing and distributing subtitle documents in the EBU-TT Live format.

FAB Subtitler - Supports EBU-TT-Live for the creation of (live) subtitles.

Subito - Captioning platform from Red Bee


(Note: With IMSC we refer to the IMSC Text-only Profile - IMSC support implies EBU-TT-D support, as it is a subset of the former.)

AppleTV and iOS - play back IMSC in fragmented MP4.

Baton - QC tool from Interra

BBC's HTML Standard Media Player - plays back EBU-TT-D.

dash.js - A reference client implementation for the playback of MPEG DASH via JavaScript and compliant browsers. Suppports IMSC.

EZtitles - Subtitling software that can be purchased or rented, supports EBU-TT-D.

FAB Subtitler - Can export in EBU-TT-D and IMSC.

Limecraft Flow - Subscription-based service for automatic creation and post-editing of subtitles, exports EBU-TT-D.

GStreamer TTML subtitling package - A means for the open source GStreamer pipelines to parse and render EBU-TT-D (TTML) subtitles.

ICE reference QC player - Marquise Technologies

imscJS - A JavaScript library for rendering IMSC1 Text and Image Profile.

R&S Clipster - Mastering system that supports IMSC

Subcheck - A commercial service from the IRT for validating IMSC subtitling files (beta version free for a limited period of time).

Subito - Red Bee supports EBU-TT-D using Subito's conversion & delivery engine.

Subtitling Conversion Framework (SCF) - A set of modules for converting subtitle formats.

take1 - Providing EBU-TT-D subtitles to a leading broadcaster.

VLC - The versatile media player has support for TTML, especially EBU-TT-D and IMSC.

If you are supporting EBU-TT and/or IMSC in your product(s) and would like to be added, send us an e-mail via: Likewise, if you spot an error in the list, please let us know via too.

* Disclaimer Above list of parties providing EBU-TT/IMSC products/tools is based on information provided by these organisations themselves, such as publicly available product specifications. Please note that the EBU does NOT verify conformance of the implementations. Inclusion in the list also does NOT mean the EBU recommends the party or its product(s)/tool(s). Users should verify the suitability of any product/tool themselves. Where tools have no clear company owner, the tool name is used.

XML Files

Informative XML sample and XML Schema files can be found via:

EBU-TT example files

EBU-TT-D W3C XML Schema - Informative EBU-TT-D XML Schema to support the implementation of EBU Tech 3380.

IRT EBU-TT-D Application Samples - EBU-TT-D sample files, related PNG images and mp4 videos showing how they should be rendered.

Related topics