Timed Text Working Group Charter

The mission of the Timed Text Working Group is to develop W3C Recommendations for media online captioning by developing and maintaining new versions of the Timed Text Markup Language (TTML) and WebVTT (Web Video Text Tracks) based on implementation experience and interoperability feedback, and the creation of semantic mappings between those languages.

Join the Timed Text Working Group.

Start date 19 May 2016
End date 31 May 2018
Confidentiality Proceedings are public
Initial Chairs Nigel Megitt,
David Singer
Initial Team Contact
(FTE %: 20)
Philippe Le Hégaret,
Thierry Michel
Usual Meeting Schedule Teleconferences: Weekly for TTML, and as needed for WebVTT
Face-to-face: 1-2 per year


This group is chartered to develop formats used for the representation of text synchronized with other timed media, like audio and video. Such formats MUST be usable for online media captioning, should be usable for described video (aka video/audio description) and should address the Media Accessibility User Requirements, and should detail any known security or privacy implications for implementers, Web authors, and end users. Such formats MAY also be usable for broadcast production and exchange and MUST be usable in the context of HTML.

The Group will:

  1. Publish a Recommendation for a new Timed Text Markup Language (TTML) 2 specification. In the process of producing this new revision, the Group:
    1. Will address any issues found during the development of a Simple Delivery Profile for Closed Captions.
    2. Will consider for adoption features from existing formats, such as CEA608 or CEA708, or developed by groups such as SMPTE, DECE and EBU.
    3. Will seek backward compatibility with TTML 1 whenever possible.
    4. Will provide a mapping with HTML5/CSS3, including describing TTML intermediate synchronic document as HTML5 document fragment, and understanding how the presentation syntax and semantics relate to CSS3.
    5. Should address the Media Accessibility User Requirements.
    6. Will take into account features added to IMSC1.
  2. Publish a Recommendation for the WebVTT language, in particular the parts that cover the syntax, semantics, and rendering of subtitles, delivery of metadata, captions, chapter markers, and textual audio descriptions for speech synthesis. The Group is expected to produce annual updates for the Recommendation with previously unspecified features.

    In the process of producing the specification, the Group:

    1. Will address any issues found in WebVTT: The Web Video Text Tracks Format produced by the Web Media Text Tracks Community Group. Some may be deferred to future versions.
    2. Will include all features that have at least two independent implementations.
    3. Should address the Media Accessibility User Requirements.
  3. Establish a semantic mapping between TTML and WebVTT in order to facilitate browser implementation and market adoption.
  4. Maintain a simple constrained profile for delivery of closed captions for video content ("TTML Simple Delivery Profile for Closed Captions (US)") for TTML.
  5. Maintain TTML 1.
  6. Publish and maintain a Recommendation for a text and an image profile of the Timed Text Markup Language (TTML) appropriate for worldwide subtitling applications (IMSC1), including dialog language translation, content description, captions for deaf and hard of hearing, etc., using TTML Text and Image Profiles for Internet Media Subtitles and Captions as basis. In the process of producing this profile the group WILL consider for adoption features from existing formats, such as CEA608 or CEA708, or developed by groups such as SMPTE, DECE and EBU.

    The Group will develop and publish a new version of IMSC that is compatible with TTML 2 and will address the concerns of backward compatibility with prior versions of IMSC.

  7. Produce a technical report (Note) on the application of TTML in live production and streaming such as for video content.
  8. Produce other technical reports (Notes) on aspects of TTML processing as appropriate.
  9. Produce a technical report (Note) on the conversion of CEA-608/708 data streams to WebVTT.
  10. Produce a technical report on how to use TTML together with the HTML5 Text Track Model. Because described concept(s) may require changes in the HTML5 specification this should be done in close collaboration with the Web Platform Working Group. It is also desirable to collaborate with the Web and TV interest group as the technical report may be of high importance for the convergence between Web and TV.

The new work is expected to be broadly available and should be provided in a timely fashion. This charter features a tightly constrained scope designed to ensure that the Working Group will meet its schedule and objectives.

Success Criteria

The Working Group is expected to demonstrate at least two independent implementations of every available new feature in the recommendations.


Other Deliverables

The Working Group will develop and update the test suites intended to promote implementations of the above specification(s), solidify the features specified, and to assess interoperability between these implementations. The Group will also produce an implementation report for each deliverable on the Recommendation track.


The Timed Text Working Group will publish milestone plans on or linked from its wiki.


For all specifications, this Working Group will seek horizontal review for accessibility, internationalization, performance, privacy, and security with the relevant Working and Interest Groups, and with the TAG. Invitation for review should be issued during each major standards-track document transition, including FPWD and CR, and should be issued when major changes occur in a specification.

W3C Groups

Web Platform Working Group
The HTML specification is intended to provide a semantic-level markup language and associated semantic-level scripting APIs for authoring accessible pages on the Web ranging from static documents to dynamic applications. It includes media elements to present video, audio and video text tracks and their associated APIs.
Accessible Platform Architectures (APA) Working Group
The mission of the Accessible Platform Architectures Working Group (APA WG) is to ensure W3C specifications provide support for accessibility to people with disabilities.
CSS Working Group
The work of the Working Group coordinates with this group on presentation and layout issues.

Liaisons with W3C Groups

Web and TV Interest Group
The Web and TV Interest Group provides a forum for Web and TV technical discussions, review existing work, as well as the relationship between services on the Web and TV services, and identifies requirements and potential solutions to ensure that the Web will function well with TV.
Web Media Text Tracks Community Group
This group developed the first Community report for the WebVTT format and will continue to explore new features.
Internationalization (i18n) Working Group
The mission of the Internationalization Working Group is to enable universal access to the World Wide Web and provide reviews of W3C technologies for internationalization issues.

External Groups

ISO/IEC JTC-1/SC-29 WG 11 Moving Picture Experts Group (MPEG)
This group is developing standards for coded representation of digital audio and video, including MPEG-4.
Society of Motion Picture and Television Engineers (SMPTE)
This organization was founded to advance theory and development in the motion imaging field. SMPTE produced extensions to TTML 1 that are part of SMPTE-TT.
European Broadcasting Union (EBU)
The EBU is an association of national broadcasting organisations, facilitating the exchange of audiovisual content. The EBU has developed EBU-TT, an XML-based format for use in subtitling production and exchange, and EBU-TT-D for use in subtitle distribution, both of which are constrained and extended variants of TTML 1.
Digital Entertainment Content Ecosystem (DECE)
DECE is a consortium chartered to develop standards for the digital distribution of premium content.
DVB Project: Technical Module (DVB-TM)
The DVB Project develops specifications for digital television systems, which are turned into standards by international standards bodies such as ETSI or CENELEC. It provides a conduit to other relevant standardisation activities including MPEG for the purpose of meeting the objectives of the DVB Project.
Advanced Television Systems Committee (ATSC)
ATSC develops standards for digital television and depends on external standards for digital closed captioning.
Association of Radio Industries and Businesses (ARIB)
ARIB develops standards relating to radiowave use in the telecommunications and broadcasting fields.


The Working Group will function as two subgroups, one for TTML and one for WebVTT, with different schedules, and coordinate when needed. For each subgroup to be successful, it is expected to have 5 or more active participants for its duration. Effective participation to a subgroup of the Timed Text Working Group is expected to consume one half-day per week for each participant; one day per week for editors. The Timed Text Working Group will allocate also the necessary resources for building Test Suites for each specification.

The group encourages questions, comments and issues on its public mailing lists and document repositories, as described in Communication.

The group also welcomes non-Members to contribute technical submissions for consideration, upon their agreement to the terms of the W3C Patent Policy.


Technical discussions for this Working Group are conducted in public. Meeting minutes from teleconference and face-to-face meetings will be archived for public review, and technical discussions and issue tracking will be conducted in a manner that can be both read and written to by the general public. Working Drafts and Editor's Drafts of specifications will be developed on a public repository, and may permit direct public contribution requests.

Information about the group (deliverables, participants, face-to-face meetings, teleconferences, etc.) is available from the Timed Text Working Group home page.

This group primarily conducts its work on the public mailing list public-tt@w3.org (archive).

The group may use a Member-confidential mailing list for administrative purposes and, at the discretion of the Chairs and members of the group, for member-only discussions in special cases when a participant requests such a discussion.

Decision Policy

This group will seek to make decisions through consensus and due process, per the W3C Process Document (section 3.3). Typically, an editor or other participant makes an initial proposal, which is then refined in discussion with members of the group and other reviewers, and consensus emerges with little formal voting being required.

However, if a decision is necessary for timely progress, but consensus is not achieved after careful consideration of the range of views presented, the Chairs may call for a group vote, and record a decision along with any objections (allowing for remote asynchronous participation -- using, for example, email and/or web-based survey techniques) and record a decision, along with any objections. The matter should then be considered resolved unless and until new information becomes available.

Any Decision taken is to be considered provisional for 10 working days after it has been recorded by the Chair and sent to the working group's mailing list. If no new objections are raised within that period, the decision will be closed. Decisions may be reopened by the Chair according to the Process Document if there is new information.

This charter is written in accordance with Section 3.4, Votes of the W3C Process Document and includes no voting procedures beyond what the Process Document requires.

Patent Policy

This Working Group operates under the W3C Patent Policy (5 February 2004 Version). To promote the widest adoption of Web standards, W3C seeks to issue Recommendations that can be implemented, according to this policy, on a Royalty-Free basis.

For more information about disclosure obligations for this group, please see the W3C Patent Policy Implementation.


For each deliverable the Working Group may choose either the W3C Document license or the W3C Software and Document license.

About this Charter

This charter for the Timed Text Working Group has been created according to section 5.2 of the Process Document. In the event of a conflict between this document or the provisions of any charter and the W3C Process, the W3C Process shall take precedence.

The previous charter is also available.

On 2018-04-05, this charter was extended from 31 March to 31 May 2018; a two-month extension to et the group continue its work while the rechartering process proceeds.