[whatwg] accessibility management for timed media elements, proposal
bhawkeslewis at googlemail.com
Sat Jun 9 08:35:01 PDT 2007
Dave Singer wrote:
> we promised to get back to the whatwg with a proposal for a way to
> handle accessibility for timed media, and here it is. sorry it took a
Three cheers for Apple for trying to tackle some of the accessibility
issues around video content! :) Without trying to assess whether CSS
media queries are the best approach generally, here's three particular
issues I wanted to raise:
1. Property values
I honestly don't think the property values are well-named. "either" is
confusing and vague; "dont-want" is a misspelled colloquialism. How
about one of the following possibilities:
(This seems more natural to me than the original proposal.)
(Has the consistency of using the same word as the basis for each value.
OTOH "prefer-not" and "no-preference" may be confusing if your English
isn't that good.)
("desire" has the minor advantages of being in Ogden's basic English
word list and being common to Romance languages thanks to a Latin root.
OTOH it's slightly longer.)
2. Conflict resolution
The proposal does not describe how conflicts such as the following would
<video ... >
<source media="all and (captions: want;high-contrast-video:
dont-want)" ... />
<source media="all and (captions: dont-want;high-contrast-video:
want)" ... />
Because style rules cascade, this sort of conflict doesn't matter when
media queries are applied to styles. But you can only view one video source.
3. (Even more) special requirements
The suggested list of media features is (self-confessedly) not
exhaustive. Here's some things that seem to be missing:
a) I should think sign-language interpretation needs to be in there.
sign-interpretation: want | dont-want | either (default: want)
Unless we want to treat sign interpretation as a special form of
subtitling. How is subtitling in various languages to be handled?
b) Would full descriptive transcriptions (e.g. for the deafblind) fit
into this media feature-based scheme or not?
transcription: want | dont-want | either (default: either)
c) How about screening out visual content dangerous to those with
photosensitive epilepsy, an problem that has just made headlines in the UK:
max-flashes-per-second: <integer> | any (default: 3)
Where the UA must not show visual content if the user is selecting for a
lower number of flashes per second. By default UAs should be configured
not to display content which breaches safety levels; the default value
should be 3 /not/ any.
d) Facilitating people with cognitive disabilities within a media query
framework is trickier. Some might prefer content which has been stripped
down to simple essentials. Some might prefer content which has extra
explanations. Some might benefit from a media query based on reading
level. Compare the discussion of assessing readability levels at:
reading-level: <integer> | basic | average | complex | any (default: any)
Where the integer would be how many years of schooling it would take an
average person to understand the content: basic could be (say) 9,
average could be 12, and complex could be 17 (post-graduate).
This wouldn't be easily testable, but it might be useful nevertheless.
Postscript: This isn't an accessibility issue but /if/ media queries are
adopted as a mechanism for serving up the best content for a person's
abilities, I wonder if they could also be used to enhance parental
control systems using queries based on PICS:
So for example, one <source> might have a music video featuring
uncensored swearing, and another <source> might have the same video with
the swearing beeped out.
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