ChangeProposal/Issue203

From HTML WG Wiki
Jump to: navigation, search

Change Proposal

All Media Elements should have the ability to have both short and longer textual descriptions associated to the element.

Summary

This Change Proposal seeks to actually make 2 changes to the current specification:

  • CP 203a - Allow media elements (<video> <audio>) to take the @alt attribute (short textual description)
  • CP 203b - Allow media elements (<video> <audio>) to take the @longdesc attribute (long textual description)

Related to:


Rationale

WCAG 2 requires that authors "Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language."

Currently, the draft HTML5 specification does not provide a native, programmatic means of associating both short and long textual descriptions to these assets, while still respecting the design need/requirement for not having those (redundant) textual descriptions on screen. Suggestions of placing that text inside of the <video> (or <audio>) element(s) does not suffice, as the specification clearly states:

"Note: 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, authors are expected to provide alternative media streams and/or
to embed accessibility  aids (such as caption or subtitle tracks, audio description tracks,
or sign-language overlays) into their media streams."

Source: http://www.w3.org/TR/html5/video.html#video


Proposal 203a - For providing the short textual description today, the current native mechanism for achieving this functionality, used on images, is the @alt attribute. The current spec states: "...the value of the alt attribute provides equivalent content for those who cannot process images or who have image loading disabled." [1] It is a seemingly obvious and rational choice to extend this attribute to the video and audio elements, which, while not images, meet the larger WCAG definition of non-text content.


Proposal 203b - For providing a longer textual description on images, the native HTML mechanism today for achieving this is the @longdesc attribute. HTML4 defines @longdesc as: "This attribute specifies a link to a long description of the image. This description should supplement the short description provided using the alt attribute." [2] If it is accepted that the @alt attribute can provide the short textual description on the media element in the same fashion that it currently does for the image element, then by extension it would be reasonable that those same media elements can reuse the same longer textual description mechanism for images: @longdesc


The following code example illustrates how these attributes could be applied to a simple video example:

<video controls
       alt="My Vacation Movie"
       longdesc="path to longer textual description which relates to the Media asset">
  <source src="vacation_movie.mp4" type="video/mp4">
  <source src="vacation_movie.webm" type="video/webm">
  <track src="vacation_captions_file.vtt" label="English captions" kind="captions">
</video>

NOTE: This Change Proposal has a dependency on the resolution of Issue 30

Details

Content attributes: NEW: add the following attributes: @alt, @longdesc


Content attributes: NEW: add the following attributes: @alt, @longdesc


Replace this:

"The image given by the src attribute is the embedded content; the value of the alt attribute provides equivalent content for those who cannot process images or who have image loading disabled.

The src attribute must be present, and must contain a valid non-empty URL potentially surrounded by spaces referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted.

{class=note}Images can thus be static bitmaps (e.g. PNGs, GIFs, JPEGs), single-page vector documents (single-page PDFs, XML files with an SVG root element), animated bitmaps (APNGs, animated GIFs), animated vector graphics (XML files with an SVG root element that use declarative SMIL animation), and so forth. However, this also precludes SVG files with script, multipage PDF files, interactive MNG files, HTML documents, plain text documents, and so forth."

With this:

"The image given by the src attribute is the embedded content. The src attribute must be present, and must contain a valid non-empty URL potentially surrounded by spaces referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted.

{class=note}Images can thus be static bitmaps (e.g. PNGs, GIFs, JPEGs), single-page vector documents (single-page PDFs, XML files with an SVG root element), animated bitmaps (APNGs, animated GIFs), animated vector graphics (XML files with an SVG root element that use declarative SMIL animation), canvas, and so forth. However, this also precludes SVG files with script, multipage PDF files, interactive MNG files, HTML documents, plain text documents, and so forth.

The the alt attribute provides an equivalent short label for any non-text content, so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language."


Replace this:

"The media element attributes, src, preload, autoplay, mediagroup, loop, muted, and controls,

apply to all media elements. They are defined in this section."

With this:

"The media element attributes, src, alt, longdesc, preload, autoplay, mediagroup, loop, muted,

and controls, apply to all media elements. They are defined in this section."


NEW: Add the following definitions for these attributes:

alt: The the alt attribute provides an equivalent short label for any non-text content, so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language. Also, when images are turned off or disabled, elements that support the alt attribute MUST render the short label defined by the alt attribute.

longdesc: The longdesc attribute may be present. This attribute contains a link to a long description of the image. If present, it must contain a valid non-empty URL potentially surrounded by spaces.

Web authors are encouraged to use this attribute for long text alternatives that are either too long to be included in the main flow of the document or benefit from structured markup that cannot be included in an alt attribute.

To obtain the corresponding long text alternative link, the value of the attribute must be resolved relative to the element. The link must point to either a different document from the image or a fragment of the same document that does not contain the image. User agents should allow users to access long text alternatives in a device independent manner. Rendering examples are provided in the rendering section.

The longdesc IDL attribute must reflect the element's longdesc content attribute.

{class=note} When the long description is included in a separate Web page, this page can then be reused for all occurrences of the image on the Website. If the separate Web page contains any additional information besides the long description, the longdesc URL needs to contain a fragment address to the particular section on that page that contains the long description. This will provide users direct access to the description.

(NOTE: Location/placement of these definitions in the specification at the discretion of the editor)

Impact

Positive Effects

Negative Effects

  • None

Conformance Classes Changes

  • Unknown

Risks

* This Change Proposal has a dependency on the resolution of Issue 30

References