ISSUE188/GenericTextTrack

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Change Proposal

Summary

Text tracks in HTML should be defined in a generic way, agnostic of a specific caption format.

A number of html elements (img, video, audio) point to content (images, videos and audio) in other resources (files); these resources have to be downloaded, decoded and displayed by the user agent as part of the web page. The format of these resources are not defined in the HTML5 specification, but rather in their relevant standards bodies, as these format are generally used in more than just a HTML5 context.

The same is true of the caption file that the track element (src attribute) points to; the WebVTT file format will be used in more than just the HTML5 context: http://lists.w3.org/Archives/Public/public-texttracks/2011Nov/0022.html http://lists.w3.org/Archives/Public/public-texttracks/2011Dec/0027.html

The HTML5 specification does not mandate, require or specify an image, video or audio format. This issue requests that the track element spec text likewise not mandate or specify the core functioning or rendering of a particular caption file format.

Rationale

The HTML5 spec currently contains a large amount of normative text for WebVTT rendering behavior. This format is more fully specified elsewhere (http://www.w3.org/community/texttracks/) and is still under active development (See the amount of mail traffic in the group).

Additionally, the WebVTT file format will not be able to support all captioning scenarios in all solutions. Like images, various interoperable improvements for various scenarios will emerge, as they did with images (GIF, PNG, JPG have distinct use cases.)

It is therefore requested that the HTML5 specification should not mandate, require or specify a caption file format.

Details

Move section 10.4.2.1 (WebVTT cue text rendering rules) to the W3C WebVTT specification.

Move section 10.4.2.2 to the W3C WebVTT specification.

Move section 10.4.2.3 to the W3C WebVTT specification.


Rewrite the accessibility note at 4.8.6 The video element:

In particular, this content is not intended to address accessibility concerns. To make video content accessible to the blind, deaf, and those with other physical or cognitive disabilities, a variety of features are available. Captions can be provided, either embedded in the video stream or as external files using the track element. Sign-language tracks can be provided, again either embedded in the video stream or by synchronizing multiple video elements using the mediagroup attribute or a MediaController object. Audio descriptions can be provided, either as a separate track embedded in the video stream, or a separate audio track in an audio element slaved to the same controller as the video element(s), or in text form using a caption file referenced using the track element and synthesized into speech by the user agent. Caption files can also be used to provide chapter titles. For users who would rather not use a media element at all, transcripts or other textual alternatives can be provided by simply linking to them in the prose near the video element.


Rewrite the accessibility note at 4.8.7 The audio element

In particular, this content is not intended to address accessibility concerns. To make audio content accessible to the deaf or to those with other physical or cognitive disabilities, a variety of features are available. If captions or a sign language video are available, the video element can be used instead of the audio element to play the audio, allowing users to enable the visual alternatives. Chapter titles can be provided to aid navigation, using the track element and a caption file. And, naturally, transcripts or other textual alternatives can be provided by simply linking to them in the prose near the audio element.


Impact

Positive Effects

WebVTT functionality and rendering is specified in the appropriate place.

This change enables continuing development of captioning scenarios and file format improvements

Negative Effects

None identified. All implementers have already shipped or expressed support for WebVTT.


Conformance Classes Changes

None identified

Risks

None identified