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Re: SMIL: draft items for UA guidelines

From: Lloyd Rutledge <Lloyd.Rutledge@cwi.nl>
Date: Thu, 01 Oct 1998 10:43:00 +0200
Message-Id: <UTC199810010843.KAA17047.lloyd@klipper.cwi.nl>
To: Judy Brewer <jbrewer@w3.org>
cc: w3c-wai-ua@w3.org, Jon Gunderson <jongund@staff.uiuc.edu>, allan_jm@tsb1.tsbvi.edu, hoschka@w3.org, kerscher@montana.com, cindy.king@gallaudet.edu, robla@real.com, Dick.Bulterman@cwi.nl, Lynda.Hardman@cwi.nl, Lloyd.Rutledge@cwi.nl, Geoff_Freed@wgbh.org

On Wed, Sep 30 1998 Judy Brewer wrote:
> > > 8. User should be able to reposition captions. [Priority two]
> > > - Rationale: Some multi-media presentations will include positioning
> > > conflicts between captions which can obscure key visual elements of video
> > > media objects.
> > > - Technique: Provide mechanisms to control caption display location
> > > dynamically and through user preferences.
> > 
> > This could be handled by switch statements that choose between
> > alternate screen layout specifications whose selection is based on
> > SMIL test attributes that refer to user characteristics, such as
> > system-captions and the system-audio-desc attribute proposed in this
> > message.
> #8. Repositioning of captions could be handled by switch statements... --
> Unclear here. Would captions that are overlaid on video media object be
> controllable in this manner, or is the idea that user preferences should
> require captions to be displayed elsewhere than on top of a video media
> object?

The switch statement described above chooses between a layout without
captions and another layout with captions.  Here, both layouts are
specified by the author, not the user.  This enables both layouts with
the look-and-feel the author desires, which would include making sure
not visual conflicts occur.  What the user has control over is simply
which layout to use.  This author-centered adaptation is based on the
perception that proper overall layout for all adaptation is best
handled by the author because it is (currently) too complex a problem
(though it is the topic of some current research) to have the system
figure out at runtime to reconfigure the layout in a way that avoid
conflicts when the user places a screen object at any position.

But one can have a special place for captions in a presentation
system, perhaps a separate window, for example.  One way to extend
SMIL to handle such presentation-time inclusion and positioning of
media is with the idea of "channels".  Rather than, or perhaps in
addition to, being placed in a layout region, captioning could be
assigned to a channel, which represents an abstract presentation
peripheral.  At presentation time the system decides how to handle
this and other types of channels.  Channels enable a lot of adaptation
and could solve other accessibility problems as well if introduced
into SMIL.


Lloyd Rutledge                                         vox: +31 20 592 41 27
CWI (Centrum voor Wiskunde en Informatica)             fax: +31 20 592 41 99
Kruislaan 413,  NL-1098 SJ Amsterdam, The Netherlands  net: lloyd@cwi.nl
P.O. Box 94079, NL-1090 GB Amsterdam, The Netherlands  http://www.cwi.nl/~lloyd
Received on Thursday, 1 October 1998 04:44:07 UTC

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