Today’s distribution platforms offer a higher quality display of subtitling and more flexible positioning options than traditional analogue television. File- and IP-based production facilities demand clearly specified ways to carry subtitles during production, exchange, archiving and distribution to their customers, including the use of online services. To handle these new contexts, broadcasters need a low-complexity, but thoroughly specified subtitling format.
To meet these requirements, the EBU Group 'Subtitles in XML' 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 2: STL mapping
EBU-TT Part 2 (EBU Tech 3360) is a mapping guide on how to map EBU STL files to EBU-TT.
EBU-TT Part M
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 http://ebu.github.io/ebu-tt-live-toolkit/ 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, and Freeview Play.
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
Also check out this list of existing open source subtitling software and samples.
EBU Project Group on Subtitles in XML
Technical aspects of subtitling are being addressed by the EBU Group 'Subtitles in XML', which is part of the EBU's Strategic Programme on Video Systems.
- Helps Members to use subtitles in new file-based facilities and for new distribution platforms.
- Develops broadcast specifications based on the W3C Timed Text Markup Language (TTML).
- Provides mappings and example files to help you use the format for subtitling.
Toolkit for Live Subtitling
The EBU has set up an open source software project to develop an Interoperability Toolkit for live subtitles. This toolkit will both validate the specification and help developers to verify that their implementations meet the specification and are interoperable. If you would like to participate in this project, please feel welcome! There is no requirement to be a member of the EBU or the Subtitles in XML Group.
If you are interested in Subtitles in XML, join our group on this topic and participate in the discussions.
EBU Technology & Innovation Workplan
Every two years, the EBU develops a roadmap for technology and innovation activities based on the requirements and inputs given by EBU Members. The result of this roadmap is our bi-annual EBU Technology & Innovation Workplan. Strategic programmes and project groups are set up to focus on specific areas of interest. To access the latest Workplan, click here.
With the publication of five new or updated EBU-TT specifications, the format now covers the complete chain from authoring to distribution, both for live...
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The MPEG-DASH Industry Forum has released v1.5 of the dash.js reference player, including support for the EBU-TT-D subtitling format, The EBU has published...
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The BBC R&D's testing has shown EBU-TT-D provides the necessary functionality to allow end-to-end subtitle streaming. The MPD and encoded segments are...
This specifies an XML based format for the distribution of subtitles over IP-based networks. It includes two additional features defined in W3C IMSC v1.0.1 and improves compatibility with other profiles of TTML by clarifying the required processor behaviour in the presence of unrecognised attributes.
For Public Service Media access services such as subtitling are very important. The formats used for its creation and distribution are evolving.
This document is Part 3 of the EBU-TT series. It specifies how to use EBU-TT for the production and contribution of live subtitles. This is version 1.0.
This document provides strategies for the mapping of EBU STL (Tech 3264) to EBU-TT Subtitle Files.
This document contains the formal definitions for metadata elements that can be used within EBU‑TT documents to describe characteristics of the contained subtitle data, thus facilitating interchange between users of an EBU‑TT document.
This is the specification of an XML based archiving and interchange format for EBU-TT subtitles. Version 1.2 provides continued alignment with the related EBU-TT specs. Note that the EBU-TT mettadata has been moved to EBU-TT part M.
This document describes how EBU‑TT Live documents (EBU Tech 3370) can be carried from node to node using WebSocket connections.
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EBU Timed Text (EBU-TT) is the successor of the EBU STL subtitling format. It supports the production and archiving of subtitles, legacy STL file transcoding and tunnelling, online distribution and live subtitling.
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This is version 1.0 of the document, dated October 2014. The aim of the document is to specify how the EBU-TT-D subtitling distribution format specified in EBU Tech 3380 can be stored using the storage format defined in ISO/IEC 14496-12.
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NPO, the Netherlands public broadcasting organization, has implemented an Optical Character Recognition (OCR) solution for real time conversion of in-vision subtitles to spoken subtitling audio.
The means of transporting subtitles & captions using MXF (the de-facto standard for A/V essence) in IT-based television production environments is specified.
This article explores some of the whats and hows of Access Services – what do prepared subtitling, live subtitling, audio description, spoken subtitling and visual signing entail ... what kinds of issues emerge when offering access services ... and how can these production and delivery issues be addressed by broadcasters.
Teletext is about 25 years old and is currently being brought into the digital broadcasting environment by the DVB project. This article looks at some of the key issues involved in offering teletext and subtitling to DVB viewers.
Subtitling has become one of the "growth areas" of European broadcasting, as television services take in increasing numbers of programmes from outside their own countries. The EBU has taken the initiative of establishing a standard for the exchange of subtitle lists.
This document specifies a format for the exchange of subtitling data. The EBU standardised this data file format to enable the exchange of in- vision and teletext subtitles. The format was designed for use by broadcasters at both national and international levels.
Informative XML sample and XML Schema files can be found via:
We are also aware of the following EBU-TT related open source projects:
- EBU-TT-D Subtitling within dash.js - The original fork of dash.js to experiment with XML based subtitles like EBU-TT-D within dash.js. Uses an HTML/CSS overlay. Has since been integrated into dash.js.
- EBU-TT-D W3C XML Schema - Informative EBU-TT-D XML Schema to support the implementation of EBU Tech 3380.
- EBU-TT Live Interoperability Toolkit - A set of components for generating, testing and distributing subtitle documents in the EBU-TT Live format.
- GStreamer TTML subtitling package - A means for GStreamer pipelines to parse and render EBU-TT-D (TTML) subtitles.
- IRT EBU-TT-D Application Samples - EBU-TT-D sample files, related PNG images and mp4 videos showing how they should be rendered.
- Subtitling Conversion Framework (SCF) - A set of modules for converting subtitle formats. Main target is the conversion of EBU STL and EBU-TT subtitle files. Alpha release.
More software projects
The EBU collects links to media-related open source software projects: media-related open source software