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.

Start date 30 May 2018
End date 31 May 2020
Charter extension See Change History.
Chairs Nigel Megitt,
David Singer
Team Contacts Thierry Michel (0.3 FTE)
Meeting Schedule Teleconferences: Weekly for TTML, and as needed for WebVTT.
Face-to-face: we will meet during the W3C's annual Technical Plenary week; additional face-to-face meetings may be scheduled by consent of the participants, usually no more than 3 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 SHOULD:

  1. Publish a Recommendation for a new Timed Text Markup Language 2 (TTML2) specification. In the process of producing this new revision, the Group SHOULD:
    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. Consider backward compatibility with TTML1 such as:
      - A conforming TTML1 content document instance is a conforming TTML2 content document instance.
      - A conforming TTML2 processor processes a conforming TTML1 content document instance such that the output produced by the TTML2 processor is within the variations allowed per TTML1; however, it may emit warnings if it encounters deprecated features.
    4. Facilitate mapping to HTML5/CSS3.
    5. Should address the Media Accessibility User Requirements.
  2. Publish Recommendations of new versions of TTML Profiles for Internet Media Subtitles and Captions 1.0.1 (IMSC1.0.1) and TTML Profiles for Internet Media Subtitles and Captions 1.1 (IMSC1.1) specifications subtitle and caption delivery applications worldwide, including dialog language translation, content description, captions for the deaf and hard of hearing, based on TTML Profiles for Internet Media Subtitles and Captions 1.0 (IMSC1), W3C Recommendation
  3. 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 have a maintenance process that produces new versions of WebVTT annually, potentially adding new features to the specification. In the process of producing the specification, the Group SHOULD:
    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. Address the Media Accessibility User Requirements.
  4. Maintain TTML1 and IMSC1 Recommendations as needed.
  5. Produce other technical reports (Notes) on aspects of TTML processing as appropriate.
  6. Liaise with other organisations including but not limited to those listed in § 3.2.
  7. Investigate caption format requirements for 360 Degree, AR and VR video content.

Success Criteria

In order to advance to Proposed Recommendation, each specification is expected to have at least two independent implementations of each of feature defined in the specification.

Each specification should contain a section discussing security and privacy.

A testing plan should be associated with each specification, starting from the earliest draft.


More detailed milestones and updated publication schedules are available on the group publication status page.

Draft state indicates the state of the deliverable at the time of the charter approval. Expected completion indicates when the deliverable is projected to become a Recommendation, or otherwise reach a stable state.

Normative Specifications

Timed Text Markup Language 2 (TTML2)
This specification defines a content type that represents timed text media for the purpose of interchange among authoring, distribution and playback systems. Timed text is textual information that is intrinsically or extrinsically associated with timing information.

Draft state: Candidate Recommendation

Expected completion: [Q4-2018]

Adopted Working Draft: Timed Text Markup Language 2 (TTML2), Candidate Recommendation, 13 March 2018.

Reference Draft: Timed Text Markup Language 2 (TTML2), Candidate Recommendation, 13 March 2018
Associated Call for Exclusion on 13 March 2018, Exclusion opportunity will end on 12 May 2018
Produced under 2016 Working Group Charter

TTML Profiles for Internet Media Subtitles and Captions 1.1 (IMSC1.1)

This specification defines two profiles of [TTML2]: a text-only profile and an image-only profile. These profiles are intended to be used across subtitle and caption delivery applications worldwide, thereby simplifying interoperability, consistent rendering and conversion to other subtitling and captioning formats. This specification improves on [ttml-imsc1.0.1] by supporting contemporary practices, while retaining compatibility with [ ttml-imsc1.0.1] documents.

Draft state: Candidate Recommendation

Expected completion: [Q4-2018]

Adopted Working Draft: TTML Profiles for Internet Media Subtitles and Captions 1.1 (IMSC1.1), Candidate Recommendation - 03 May 2018

Reference Draft: TTML Profiles for Internet Media Subtitles and Captions 1.1 (IMSC1.1), Candidate Recommendation - 03 May 2018
Associated Call for Exclusion on 3 May 2018 ending on 2 July 2018
Produced under 2016 Working Group Charter

WebVTT: The Web Video Text Tracks Format

This specification defines WebVTT, the Web Video Text Tracks format. Its main use is for marking up external text track resources in connection with the HTML <track> element. WebVTT files provide captions or subtitles for video content, and also text video descriptions [MAUR], chapters for content navigation, and more generally any form of metadata that is time-aligned with audio or video content.

Draft state: Candidate Recommendation

Expected completion: [Q1-2019]

Adopted Working Draft: WebVTT: The Web Video Text Tracks Format, Candidate Recommendation 10 May 2018

Reference Draft: WebVTT: The Web Video Text Tracks Format, Candidate Recommendation 10 May 2018
Associated Call for Exclusion on 10 May 2018, ending on 9 July 2018
Produced under 2016 Working Group Charter

The Working Group may update the following W3C Recommendations, as needed:

Other Deliverables

Other documents may be created such as:

  • Use case and requirement documents;
  • Test suite and implementation report for the specification;
  • Specifications snapshots;
  • Primer or Best Practice documents to support web developers when designing applications;
  • Working Group Notes as needed;
  • Mapping to HTML5/CSS3.

Other documents may be updated such as:

As needed, the Group will also coordinate with the HTML Accessibility Task Force and the Web Platform Working Group to contribute how to interoperably implement described video with the Open Web Platform.

Development of deliverables

All substantive changes to specifications should have associated tests.


  • May 2018: First teleconference
  • Oct 2018: face-to-face meeting during TPAC
  • June 2018: TTML2 Candidate Rec (second version)
  • Sept 2018: TTML2 Proposed Rec
  • Oct 2018: TTML2 Recommendation
  • Sept 2018: IMSC 1.1 Proposed Rec
  • Oct 2018: IMSC 1.1 Recommendation
  • December 2018: WebVTT Proposed Rec
  • January 2019: WebVTT Recommendation


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 must be issued during each major standards-track document transition, including FPWD, and should be issued at least 3 months before CR, and should be issued when major changes occur in a specification.

Additional technical coordination with the following Groups will be made, per the W3C Process Document:

W3C Groups

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.
Media and Entertainment Interest Group
The Media and Entertainment 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.
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.

The Working Group will consider inputs provided by Community Groups, including Web Platform Incubator Community Group (WICG) for example to add new features.

External Organizations

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 TTML1 that are part of SMPTE-TT.
European Broadcasting Union (EBU)
The EBU is an association of national broadcasting organizations, 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 TTML1.
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.


To be successful, this Working Group is expected to have 6 or more active participants for its duration, including representatives from the key implementors of this specification, and active Editors and Test Leads for each specification. The Chairs, specification Editors, and Test Leads are expected to contribute half of a working day per week towards the Working Group. There is no minimum requirement for other Participants.

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: the 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. The meetings themselves are not open to public participation, however.

Information about the group (including details about deliverables, issues, actions, status, participants, and meetings) will be available from the Timed Text Working Group home page.

Most Timed Text Working Group teleconferences will focus on discussion of particular specifications, and will be conducted on an as-needed basis.

This group primarily conducts its technical work on the public mailing list public-tt@w3.org (archive) or GitHub issues. The public is invited to review, discuss and contribute to this work.

The group may use a Member-confidential mailing list member-tt@w3.org (archive) 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.

To afford asynchronous decisions and organizational deliberation, any resolution (including publication decisions) taken in a face-to-face meeting or teleconference will be considered provisional. A call for consensus (CfC) will be issued for all resolutions (for example, via email and/or web-based survey), with a response period of 10 working days. If no objections are raised on the mailing list by the end of the response period, the resolution will be considered to have consensus as a resolution of the Working Group.

All decisions made by the group should be considered resolved unless and until new information becomes available, or unless reopened at the discretion of the Chairs or the Director.

This charter is written in accordance with the W3C Process Document (Section 3.4, Votes), 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 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.

Charter History

The following table lists details of all changes from the initial charter, per the W3C Process Document (section 5.2.3):

Charter Period Start Date End Date Changes
Initial Charter 2008-08-15 2010-06-30 Restarted the Working Group
Charter Extension 2011-03-31 none
Rechartered 2012-07-25 2014-01-31 TTML 1.0 2nd edition, TTML 1.1
Rechartered 2014-03-27 2016-03-30 WebVTT 1.0, IMSC 1.0
Charter Extension 2016-05-31 none
Rechartered 2016-05-19 2018-03-31 none
Charter Extension 2018-05-31 none
Rechartered 2018-05-30 2020-05-31 none