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Re: (Action): Proposals and questions about "presentations" and "animations" [Issue 430]

From: Charles McCathieNevile <charles@w3.org>
Date: Thu, 25 Jan 2001 01:23:55 -0500 (EST)
To: Ian Jacobs <ij@w3.org>
cc: <w3c-wai-ua@w3.org>
Message-ID: <Pine.LNX.4.30.0101250112040.24130-100000@tux.w3.org>
On Wed, 24 Jan 2001, Ian Jacobs wrote:

  Proposal 1: Delete the formal term "presentation"

CMN I support the proposal

Also note that presentation is used in a different sense in WCAG (as an
abstract noun, rather than as a concrete noun, for people who like technical
terms). It would be easiest not to have two different uses in different

  Proposal 2: About animations

  Suppose for the proposals below that the definition of "animation"
  includes "animated images".

  Proposal 3: Checkpoint 3.2

  1) Do not broaden checkpoint 3.2 to include other animations
     than animated images:

       Allow the user to configure the user agent not to render
       audio, video, or animated images except on explicit request
       from the user.  In this configuration, provide an option to
       render a placeholder in context for each unrendered source
       of audio, video, or animated image. When placeholders are
       rendered, allow the user to activate each placeholder
       individually and replace it with the original
       author-supplied content. [Priority 1]

    Rationale: The "placeholder" requirements of 3.2 make it
    difficult to imagine how this would be done for animations
    in general, created through scripts, style sheets, and
    markup languages. Note also that the user can control a more
    general class of animations per the requirements of Guideline 4.

  2) Change the content type label from "Animation" to "Image"
     (since this is only about animated images).
CMN I am happy about the proposal, subject to my concerns about checkpoints
in guideline 4 - see below.

  Proposal 4: Checkpoint 3.4
CMN Don't care either way

  Question about checkpoints 4.4/4.5/4.7/4.8

  Question: For checkpoints 4.4 and 4.5, are these checkpoints
  intended to require control of synchronized multimedia
  presentations?  Here are the checkpoints:

CMN I have responded to the question asked below. But in following up my
action item from a couple of weeks ago, I think these checkpoints should also
provide for step-by-step motion through a time-based presentation, including
the more complex types of animation avalable in SMIL 2 and SVG (and languages
that incorporate the animation features, such as XHTML family languages). I
don't think this represents a change in intent, although it does represent a
clarification of a point that may not have been universally understood to be
like this.

back to the normal programming:
   4.4 Allow the user to slow the presentation rate of audio,
   video and animations. For a visual track, provide at least
   one setting between 40% and 60% of the original speed. For a
   prerecorded audio track including audio-only presentations,
   provide at least one setting between 75% and 80% of the
   original speed. When the user agent allows the user to slow
   the visual track of a synchronized multimedia presentation
   to between 100% and 80% of its original speed, synchronize
   the visual and audio tracks. Below 80%, the user agent is
   not required to render the audio track. The user agent is
   not required to satisfy this checkpoint for audio, video and
   animations whose recognized role is to create a purely
   stylistic effect. [Priority 1]

   4.5 Allow the user to stop, pause, resume, fast advance, and
   fast reverse audio, video, and animations that last three or
   more seconds at their default playback rate.  The user agent
   is not required to satisfy this checkpoint for audio, video
   and animations whose recognized role is to create a purely
   stylistic effect. [Priority 1]

  Note also checkpoint 2.5:

   2.5 Respect author-specified synchronization cues during

  This means that if the user slows down audio per checkpoint
  4.4 and that audio is part of a synchronized presentation, then
  the user agent should slow down the entire presentation
  (respecting synchronization cues). Do other people have
  the same understanding?

CMN Yes. There may be times when this makes some content difficult to
understand. For example, going through a video at varied speeds to understand
fastest what is being presented visually may make the sound more or less
incomprehensible. This would then require a user to work out what is
happening in the video, and go through it again to get the sound, doing a
sort of mental mix. (This is the kind fo things cinema fans are known to do
for particularly important pieces of film, and TV shows do a lot to
demonstrate where there is an anamoly or continuity failure.) I don't see
this as a problem, although it may be best to point it out explicitly.
Otherwise someone might say "but if we slow the video then the audio won't
make sense, so it is a bad idea", or vice versa.

  1) If 4.4 (and/or 4.5) includes control over synchronized content,
     should we make this clearer, or is the cross reference to
     checkpoint 2.5 sufficient?

I think the cross reference is sufficient, and that it does apply in general.
in other words I think that in this respect the present version is


Charles McCN

  2) If 4.4 (and/or  4.5) does not include control over
     synchronized content and only is about individual source sof
     video, audio, or animation, then should we make this clearer?

  I don't have a proposal for changing 4.4 and 4.5; I await
  feedback from the WG.


   - If animated images are a subclass of animations, then
     checkpoints 4.4, 4.5, 4.7, and 4.8 require addition of
     the "Image" content type label.

Charles McCathieNevile    http://www.w3.org/People/Charles  phone: +61 409 134 136
W3C Web Accessibility Initiative     http://www.w3.org/WAI    fax: +1 617 258 5999
Location: I-cubed, 110 Victoria Street, Carlton VIC 3053, Australia
(or W3C INRIA, Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex, France)
Received on Thursday, 25 January 2001 01:23:56 UTC

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