- From: Ian Jacobs <ij@w3.org>
- Date: Mon, 26 Jun 2000 00:40:01 -0400
- To: w3c-wai-ua@w3.org
Hello, This message is an attempt to capture some of the discussion between Charles McCathieNevile, Eric Hansen, and myself about some of the concepts related to multimedia that are part of the UA Guidelines. The purpose of this message is primarily to document some issues raised during that discussion. I don't speak here on behalf of Eric or Charles. The message is not entirely coherent, but I wanted to get some notes out to the Working Group. There is a semblance of a proposal (of definitions) at the end of the email. The goal of this email is to contribute to the effort to answer some questions about definitions of terms related to multimedia. Eric has already sent a number of emails on this topic ([2], [3], [4]). Three definitions in the 10 June Guidelines [1] relate to multimedia: auditory presentation, multimedia presentation, and synchronize. We also use the following terms but do not defined them: auditory track, visual track. [1] http://www.w3.org/WAI/UA/WD-UAAG10-20000610 [2] History and Meaning of the term "Multimedia" http://lists.w3.org/Archives/Public/w3c-wai-ua/2000AprJun/0503.html [3] Definitions of Visual Track and Auditory Track, Etc. http://lists.w3.org/Archives/Public/w3c-wai-ua/2000AprJun/0374.html [4] Comments on multimedia and audio http://lists.w3.org/Archives/Public/w3c-wai-gl/1999OctDec/0290.html In our telephone discussion, we considered how a number of "axes" might impact definitions of terms related to multimedia. Here are the axes: - Content type v. rendering modality (audio, video, tactile) - Stand-alone v. complementary - Primary v. alternative content - Static v. dynamic - Synchronized v. unsynchronized - Distinguishable tracks Below is a little bit of exposition on the axes. 1) Source or Rendering? When we say something like "allow the user to freeze animations", we are probably referring to content that is rendered as an animation, whatever the format of the content. So, an animation may be the result of an animated gif or SVG animation, the effect of a script, or the application of a style sheet to text. If we consider rendering rather than source format, the key terms we should be using relate to the senses: auditory, visual, and tactile. Our definitions should be oriented towards how the content is received. 2) Dynamic content. Content may evolve in different ways over time: a) A static HTML page does not evolve. b) A dynamic HTML page may change or evolve under the effect of scripts. c) Audio and video have natural time components. Questions: - To what extent is a multimedia presentation required to change over time? For instance, is a static HTML page with background audio playing a "degenerate" multimedia presentation? - Does a multimedia presentation necessarily require the synchronization of components? What if I have a page of images, I select a link to play an audio clip, and I select another link to view a video clip. Is this a multimedia presentation? 2) Stand-alone versus complementary. When an author produces content, some components may serve complementary purposes while others may serve equivalent purposes. For instance, in a television program, while the visual information and auditory information are certainly related, they are not equivalents for one another. Recall that an auditory equivalent for the visual track of a presentation is an audio track plus a synchronized auditory description of the visual information. Other components of content may be (functional) equivalents of on another (e.g., text captions are the text equivalent of the audio track). It might be possible to define a multimedia presentation as: a) A presentation that includes both visual tracks and audio tracks. b) These tracks complement each other. A stand-alone presentation is one that does not require a complement to convey its message. For instance, a radio program is a stand-alone auditory presentation. Based on these definitions, a radio program would not be consider a multimedia presentation, even if the radio program were accompanied by equivalents. Similarly, a radio program with an accompanying video track of signing hands would not be a multimedia presentation since the visual track is a functional equivalent of the audio. Alternatives form a unit in a different way than multimedia components form a unit. I think it's possible to talk about "primary content" and its alternatives as a unit. "Primary" probably means what the author intends to be rendered most of the time. 3) Presentation versus Track a) Based on the previous discussion of "complementary" components, the term presentation would refer to a "complete" presentation (all necessary components included, be they stand-alone or multimedia, with alternative equivalents considered separately). b) The term "track" would refer to either a video or and audio track of a multimedia presentation. However, if a static HTML page plus background audio is considered a multimedia presentation, then calling the static page a "track" seems odd. Calling the background audio a track seems less odd to me. c) With some formats, user agents can distinguish tracks, with others, they may not be able to (e.g., a SMIL presentation with discernible tracks versus a single mixed audio source). Proposal: 1) Start with basic components in terms of rendering, not source format: <DEF> Visually rendered content: any content rendered for the visual sense. This would have to include images, text, video, scripts that produce visual effects, style sheets that produce visual effects, etc. </DEF> <DEF> auditorily rendered content: any content rendered for the visual sense. This includes text rendered as speech, pre-recorded audio, etc. </DEF> 2) Introduce stand-alone v. track: <DEF> Stand-alone audio presentation: Auditorily rendered dynamic content that conveys a message without requiring additional content. Note that stand-alone audio presentations require alternatives so that they will be accessible to some users. </DEF> <DEF> Stand-alone video presentation: Visually rendered dynamic content that conveys a message without requiring additional content. Note that stand-alone video presentations require alternatives so that they will be accessible to some users. </DEF> <DEF> Auditory track: Auditorily rendered dynamic content that is functionally part of a larger presentation. Note that audio tracks require alternatives so that they will be accessible to some users. </DEF> <DEF> Visual track: visually rendered dynamic content that is functionally part of a larger presentation. Note that visual tracks require alternatives so that they will be accessible to some users. </DEF> <DEF> Synchronized multimedia presentation: A presentation consisting of at least one auditory track that is synchronized with a visual track. Note that tracks of a multimedia presentation require alternatives so that they will be accessible to some users. </DEF> Notes and questions; - Where does animation fit? - The term "dynamic content" needs to be clarified. - Part of the discussion involved trying to fit static content plus background audio into a larger definition. Trying to do so may be a mistake. At the 22 June teleconference [5], Gregory took an action item to investigate requirements for configuring the user agent to not render audio on load, so I anticipate the background audio question to be resolved in light of Gregory's proposals. - When should we use "audio" and when should we use "auditory"? Same for "video" and "visual". Also, we have consciously used the term "graphical" instead of "visual" for a long time. [5] http://lists.w3.org/Archives/Public/w3c-wai-ua/2000AprJun/0505.html Your comments welcome, - Ian -- Ian Jacobs (jacobs@w3.org) http://www.w3.org/People/Jacobs Tel: +1 831 457-2842 Cell: +1 917 450-8783
Received on Monday, 26 June 2000 00:40:09 UTC