- From: Charles McCathieNevile <charles@w3.org>
- Date: Mon, 16 Aug 1999 17:19:11 -0400 (EDT)
- To: WAI UA group <w3c-wai-ua@w3.org>
Further to my action item from the last teleconference... I have grouped the topics slightly differently, since there are techniques which are applicable to all timed presentations from a user agent point of view (the ability to control the rate of the presentation, and select among multiple tracks), and because visual presentation of captions seems to be more obviously related to video presentation (although it may also be done through haptic media such as braille). Charles McCN Reference: http://www.w3.org/WAI/UA/WAI-USERAGENT-TECHS/#ua-style For controlling text and colour: Implement CSS [CSS1], [CSS2] including the CSS2 cascade order and local (user) style sheets. this will enable users to control presentation while allowing authors great flexibility. See also checkpoint 3.3 in WCAG. CSS should be implemented by user agents which render HTML, XML, SVG, and SMIL players which render text content directly. CSS includes properties for audio, braille (fixed and refreshable), screen, and print rendering, and all relevant properties for supported output media should be implemented. The CSS specification includes a mechanism for including "presentational" markup in the cascade order, which should be implemented to allow the correct functioning of a user stylesheet. A user stylesheet can be implemented using many kinds of interface, which may or may not require the user to understand how CSS works. For example, a simple set of font and colour selections can be used to generate appropriate CSS. For an example of this, see the style sheets implementation of the W3C testbed browser/editor Amaya, which provides a GUI-based interface to create and apply internal style sheets. The same technique could be used to control a user stylesheet. For controlling images, applets and animations: background images can be controlled by the use of local style sheets, and more effectively if these can be dynamically updated. Animation rate depends on the players used - where a user agent provides native rendering of animation (for example a movie player, a driver for animated GIF images, or a java machine) that player should enable the control of animation rates, or at least allow the user to stop, and to play frame-by-frame, as well as normal rendering. In the SMIL-boston working draft there is support for animation. A SMIL player could provide control of the general timing of a presentation, combined with the ability to select from available tracks manually. An issue to bear in mind is that when animation is synchrnised with audio a user may need the ability to play the animation seperately from the associated audio - see controlling audio (below). For controlling time-based presentations (audio, video, slide presentations): implement user controls to start, atop, rewind and pause presentations, and wher multiple tracks are supported, to choose which tracks should be rendered. SMIL provides a number of these features. The implementation should provide for direct user control, as well as activation of the controls through a published API, for developers of assistive technologies. For Controlling audio and speech: CSS2 audio properties include speech rate, volume, and pitch. These can be implemented by allowin the user to write and apply a local style sheet, or can be automatically generated by means of (accessible) user controls, which should also be controllable through an API. (CNM- I vaguely recall seeing an example of this implemented in Java through the Accessibility API. Has anyone else seen this, or did I make it up?) For controlling video (including captions): Implement the CSS positioning and/or SMIL layout languages. Allow the user to freeze a presentation, manually move and resize component video tracks (including captions, subtitles and signed translations) and to apply CSS stylesheets to text-based presentation and SVG. For controlling user interface: Allow the user to select large or small buttons and controls (and ensure that these values are applied consistently across the user interface) (Opera does this). Allow the user to control features such as menu font sizes, or speech rates - this may be achieved through use of operating system standards. Allow the user to regroup buttons and controls, and reorder menus (MS Word does this). (CMN This is also related to reconfiguring commands, etc.)
Received on Monday, 16 August 1999 17:19:11 UTC