**DRAFT** Timed Text Working Group Charter

The mission of the Timed Text Working Group, part of the Video in the Web Activity, 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.

End date 30 November 2015
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 useable for online media captioning, should be useable for described video (aka video/audio description) and should address the media accessibility user requirements. Such formats MAY also be useable for broadcast production and exchange and MUST be useable 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 WILL:
    1. Address any issues found during the development of a Simple Delivery Profile for Closed Captions.
    2. Consider for adoption features from existing formats, such as CEA608 or CEA708, or developed by groups such as SMPTE, DECE and EBU
    3. Produce other technical reports (Notes) on aspects of TTML processing as appropriate.
    4. Seek backward compatibility with TTML 1 whenever possible.
    5. 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.
    6. As required, produce a test suite for the above.
    7. Produce an implementation report, based on the test suite above.
  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 from browser vendors.

    In the process of producing the specification, the Group WILL:

    1. 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. Include all features that have at least two independent and interoperable implementations
    3. Solidify the set of features through the creation of a WebVTT test suite
    4. Consider the adoption of new features
  3. The group MAY decide to the use the experimental license, developed for HTML extensions, for the VTT document.
    Editororial Note: Why does this ask for permission to use the experimental license?

    The experimental license was approved only for products of the HTML working group. Though VTT is often thought of as an HTML extension (notably by the original author), this work will be going on in the more appropriate TTML working group, dedicated to Timed Text, and thus it doesn’t fall automatically into the approved category. The original version of the VTT document was developed in a Community Group, and CG deliverables have a fairly liberal license. The group is keen to avoid the problem that the CG output(s) become more used/referenced than the WG official documents, as a consequence of their more liberal license: in a sense, this would be encouraging the very forking that the W3C license normally tries to avoid. Ideally the CG output(s) are seen as, and marked as, and understood as, precursors to the WG output(s), and the WG Recommendation Track documents are seen as current and are the ones used, referenced, and so on. By using a liberal license for the WG document(s), we can avoid having the CG documents be apparently ‘more attractive’, and thus we can effectively retire them.

    (We note that this work is among the first to move from Community to Working group, and this issue may come up again.)

    If problems are found with this approach, the group will use the W3C document license, and try to handle the transition as gracefully as it can.

  4. Establish a semantic mapping between TTML and WebVTT in order to facilitate browser implementation and market adoption.
  5. Maintain a simple constrained profile for delivery of closed captions for video content ("Simple Delivery Profile for Closed Captions") for TTML.
  6. Maintain TTML 1.
  7. Publish a text and an image profile of the Timed Text Markup Language (TTML) appropriate for worldwide subtitling applications, 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.
  8. Produce a technical report (Note) on the application of TTML in live production and streaming such as for video content.
  9. Produce a technical report (Note) on the conversion of CEA-608/708 data streams to WebVTT.

The new work is expected to be broadly available and should be provided on 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 interoperable implementations of all available features in the recommendations.


Other Deliverables

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


Note: The group will document significant changes from this initial schedule on the group home page.
Deliverable LC Note CR PER PR Rec
WebVTT 1.0 January 2014 N/A March 2014 N/A September 2014 November 2014
TTML Live Production and Streaming Note March 2014 June 2014 N/A N/A N/A N/A
Timed Text Markup Language (TTML) 2 April 2014 N/A July 2014 N/A December 2014 February 2015
Text and Image Profiles for Internet Media Subtitles and Captions April 2014 N/A July 2014 N/A December 2014 February 2015
TTML/WebVTT mapping N/A September 2014 N/A N/A N/A N/A


As part of the Video in the Web Activity, the Timed Text Working Group will be represented in the Hypertext Coordination Group.

Dependencies with W3C Groups

HTML 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.
CSS Working Group
The work of the Working Group coordinates with this group on presentation and layout issues.
Protocols and Formats Working Group
The PFWG looks at the formal Web technologies (protocols, formats, etc.) from an accessibility perspective.
Web Content Accessibility Guidelines Working Group
This Group aims to make Web content accessible for people with disabilities.

Liaisons with W3C Groups

Scalable Vector Graphics (SVG) Working Group
The Scalable Vector Graphics language allows authors to describe two-dimensional vector and mixed vector/raster graphics. It includes support for multimedia: audio, video and animation.
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)
EBU is a confederation of national broadcasting organisations, facilitate exchange of audiovisual content. This Group has developed an XML -based format for use in subtitling production and exchange, based on 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.


To be successful, the Timed Text Working Group is expected to have 5 or more active participants for its duration. Effective participation to 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.

Participants are reminded of the Good Standing requirements of the W3C Process.


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

A Member-only mailing list, member-tt@w3.org (archive) is available for administrative purposes such as liaison with Member-only Working Groups.

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

Decision Policy

As explained in the Process Document (section 3.3), this group will seek to make decisions when there is consensus. When the Chair puts a question and observes dissent, after due consideration of different opinions, the Chair should record a decision (possibly after a formal vote) and any objections, and move on. 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.

About this Charter

This charter for the Timed Text Working Group has been created according to section 6.2 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.

Proposed by David Singer.

$Date: 2013-12-09 14:10:37 $