Specifications in progress

  • Beyond text tracks, Web pages may contain many other time-based animations with which synchronization can be useful; the Web Animations API offers the tools needed to set up these synchronization points. This may become the basis for the Media Overlay work both in terms of model and terminology, as well as possible implementation work.
  • Media Overlay may require some simple extensions to HTML (e.g., additional attributes for Media Overlays). The HTML Extension Specifications provides a good starting point for the roadmap to such extensions.
  • TTML2 Content may be used directly as a distribution format, for example, providing a standard content format to reference from a track element in an HTML document, or a text or textstream media element in a SMIL 3.0 document.
  • TTML Profiles for Internet Media Subtitles and Captions 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.
  • The main use of WebVTT 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 used for accessibility purposes [MAUR], chapters for content navigation, and more generally any form of metadata that is time-aligned with audio or video content.
FeatureSpecification / GroupMaturityCurrent implementations
Select browsers…
Web Animation APIWeb Animations
CSS Working Group
SVG Working Group
Working Draft
HTML ExtensionsHTML Extension Specifications
Web Platform Working Group
Editor's Draft
Timed Text Markup LanguageTimed Text Markup Language 2 (TTML2)
Timed Text Working Group
TTML Profiles for Internet Media Subtitles and CaptionsTTML Profiles for Internet Media Subtitles and Captions 1.1
Timed Text Working Group
WebVTT: The Web Video Text Tracks FormatWebVTT: The Web Video Text Tracks Format
Timed Text Working Group
Candidate Recommendation

Exploratory work

  • There are a number of cases that need synchronization of several tracks in the same page, for instance to synchronize the sign-language transcript of an audio track with its associated video. The MediaController interface, initially defined in HTML5, was dropped from the HTML specification due to very limited implementation support. The Timing Object specification proposes a mechanism to bring shared on-line locks to browsers and ease synchronization of heterogeneous content within a single device and across devices. This may be useful for the Media Overlay work.
FeatureSpecification / GroupImplementation intents
Select browsers…
Multi-device synchronizationTiming Object
Multi-Device Timing Community Group