DRAFT
2 November 1998The Web Accessibility Initiative ([WAI]) worked together with the W3C SYMM Working Group to pursue and promote accessibility in the design of [SMIL 1.0] before it became a W3C Recommendation in June 15th, 1998. The SMIL standard presented the WAI group some new challenges as it is the first W3C standard focused in creating TV like presentations by synchronizing media objects. A SMIL presentation may have a lot of temporal material, some of it is in video or audio form and some just comes from the synchronization abilities.
The main focus of the WAI group at this stage was to offer means for attaching information using alternative media to the SMIL presentations. In particular, the WAI group addressed:
In the future, there might be need to define more means for the style and layout of the whole presentation. For instance, to be able to attach a stylesheet to the whole presentation and to define the used font, font size and colors for each media object in one place. This might be possible to do with user agents.
There is work going on in defining guidelines for user agents, so that the documents including SMIL documents remain accessible. The various media object components should be accessible from user agents, also the material tied to a certain presentation time should be accessible e.g. without an ability for fine grain control of the time and the seeing the links. For instance, there may be a need to present the time dependent links in a static way, so that it is possible to browse them and possibly also see the corresponding sequences of the presentation that activate the link.
Synchronization elements in SMIL define which elements happen in parallel and which happen sequentially. Alternate content of the synchronization elements can be shown by using a TITLE attribute for a short meaningful textual description that can be used in tooltips, ABSTRACT attribute for a brief description of the media element content. and an AUTHOR attribute for describing the author of the synchronization element.
Alternate content of the media object elements can be shown by using the familiar accessibility attributes ALT for alternative text, LONGDESC for a link to a longer textual description, and TITLE for a short meaningful textual description that can be used in tooltips. In addition, a media object can have an ABSTRACT attribute, which is a brief description of the media element content. ??Why cannot we use ALT or LONGDESC? What is the difference?? The AUTHOR attribute describes the author of the media object content.
The following example contains a link from an element in one presentation A to the middle of a video object contained in another presentation B. This would play presentation B starting from second 5 in the video. The alternate text of the link in presentation A refers to the subpart of B that is being played. The alternate text of presentation B refers to the whole media object element.
Presentation A: <a href="http://www.cwi.nl/mm/presentationB#tim"> <video id="graph" src="rtsp://foo.com/graph.imf" alt="Tim's interview on Web trends" region="l_window"/> </a> Presentation B: <video src="http://www.w3.org/CoolStuff" alt="Joe's and Tim's interview for BBC"> <anchor id="joe" begin="0s" end="5s"/> <anchor id="tim" begin="5s" end="10s"/> </video>
With special attributes for captioning it is possible to add captioning information to any media object or synchronization element. Normally the media object contains audio that is captioned. The media object containing caption is marked by using an attribute SYSTEM-CAPTIONS. This attribute has value "ON" when the captionings are shown to the user and "OFF" when the user doesn't want to see captions.??Why not use stylesheets with display=none? Now the actual SMIL document is going to change dynamically when the user turns these on and off??
In the following example, captions are shown only if the user?? wants captions on.
... <seq> <par> <audio src="audio.rm"/> <video src="video.rm"/> <textstream src="stockticker.rtx"/> <textstream src="closed-caps.rtx" system-captions="on"/> </par> </seq> ...
In the following example, a French-language movie is available with English overdub and caption tracks. The following SMIL segment expresses this, and switches on the alternatives that the user?? prefers.
... <par> <switch> <audio src="movie-aud-en.rm" system-language="en" system-overdub-or-caption="overdub"/> <!-- French for others --> <audio src="movie-aud-fr.rm"/> </switch> <video src="movie-vid.rm"/> <switch> <textstream src="movie-caps-en.rtx" system-language="en" system-overdub-or-caption="caption"/> <!-- French captions for others --> <textstream src="movie-caps-fr.rtx" system-captions="on"/> </switch> </par> ...
If captioning is on, the switch statement can be possibly used to define a new layout with the captioning region. ??It would also be nice if the user could be able to make the captioning region a new window when she wishes.?? The captioning media object may use CSS stylesheets to define fonts and colors. It is not possible to attach a style sheet in the SMIL presentation, however, the default values set at the user agent can override the values set on each of these stylesheets. The only style attribute that can be set in SMIL is BACKGROUD-COLOR and without other color definitions that has little effect to accessibility.
A SMIL presentation might have anchors associated with video, that are only active at a certain time. Users should be able to get also other than visual cues that tell users that new anchors have appeared. In addition, it should be possible to search links without of the time dimension.
In the following is an example of SMIL markup that chooses between content with different bitrate. The media player evaluates each of the parallel choices (par elements) one at a time, looking for a bitrate that fits with the characteristics of the link between the media player and media server.
... <par> <text .../> <switch> <par system-bitrate="40000"> ... </par> <par system-bitrate="24000"> ... </par> <par system-bitrate="10000"> ........ </par> </switch> </par> ...
The WAI group has produced a set of guidelines for page authors. The guidelines, and related documents, describe good authoring practice in detail as it relates to accessibility.
The W3C Web Accessibility Initiative is pursuing accessibility of the Web through five primary areas of work: addressing accessibility issues in the technology of the Web; creating guidelines for browsers, authoring tools, and content creation; developing evaluation and validation tools for accessibility; conducting education and outreach; and tracking research and development. Depending on an individual's disability (or the circumstances in which one is browsing the Web, for instance on a device with no graphics display capability, or in a noisy environment), graphics, audio content, navigation options, or other aspects of Web design can present barriers.
The WAI International Program Office (IPO) enables partnering and coordination among the many stake-holders in Web accessibility: industry, disability organizations, government, and research organizations. The IPO is sponsored by the US National Science Foundation and the Department of Education's National Institute on Disability and Rehabilitation Research; the European Commission's TIDE Program, and W3C industry Members including IBM/Lotus Development Corporation, Microsoft Corporation, NCR, and Riverland Holding. Disability and research organizations on several continents also actively participate in the WAI.
The W3C was created to lead the Web to its full potential by developing common protocols that promote its evolution and ensure its interoperability. It is an international industry consortium jointly run by the MIT Laboratory for Computer Science (LCS) in the USA, the National Institute for Research in Computer Science and Control (INRIA) in France and Keio University in Japan. Services provided by the Consortium include: a repository of information about the World Wide Web for developers and users; reference code implementations to embody and promote standards; and various prototype and sample applications to demonstrate use of new technology. To date, more than 235 organizations are Members of the Consortium.
For more information about the World Wide Web Consortium, see http://www.w3.org/
A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR.
The authors welcome comments:
Marja-Riitta Koivunen (marja@w3.org)
Director, Web Accessibility Initiative International Program Office
World Wide Web Consortium (W3C)
MIT/LCS Room NE43-355
545 Technology Square, Cambridge MA 02139 USA
1 (617) 258-9741
http://www.w3.org/WAI