Timed Media Accessibility:
Surveying the terrain
David Singer, with help from the web
media team
Apple Inc.
INTRODUCTION
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The 3 legs of good accessibility
• Specifications and tutorials
• Authors
• Users and user agents
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Dream: do better than than TV
• Good framework for accessibility
– immediate needs
– innovation and increasingly effective future
provisions
• Use web technologies
• Use preferences
• Be bright!
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The problem space
• Timed accessibility
– captions, audio, sign language
• Untimed accessibility
– transcripts, alternatives
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TIMED ACCESSIBILITY
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Audio
•
•
•
•
Captions
(Subtitles)
Sign language
Contrast etc. issues
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Video
• Audible description of video
• Contrast etc. issues
• Seizure avoidance (e.g. Epilepsy susceptibility)
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General and Time Management
• ‘Slide-flipping’ in parallel with the media
• Rate preferences (e.g. normally at 80%)
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UNTIMED ACCESSIBILITY
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Two un-timed challenges
• Links to transcripts
• Alternative, longdesc and fallback content
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INSIDE OR OUTSIDE THE MEDIA
CONTAINER?
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Inside
•
•
•
•
Burned-in (open) captions
‘Overlay’ Timed text tracks
Audio narration (description)
Sign-language (video) tracks
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Outside
• Captions – scripted or second player
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MEETING NEEDS
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Handling timed accessibility
• select the resource which has or can have the
provision needed
• configure it if it’s an optional feature
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User selection
• By preference
• By action
• Either/Both?
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Hypothesis
• ‘Somewhere’ there can be user preferences
• Axes:
– Captions (subtitles?)
– Audio description of video
– Sign language
– Seizure avoidance, contrast, etc.
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Source selection
• Use <source> media query
• Allow it to enquire the user’s presentational
needs
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Discussion
• Simple rules: match prefs-source FAILS if either:
– user has a need, and the source says it explicitly does
not support it
– user does not have a need, and the file is tagged to
support it
• Second rule is needed so users not wanting
(mentioning) a need will skip sources tagged as
explicitly for it (e.g. open captions)
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In Tabular Form
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I want need X
satisfied
I don’t mention
need X
targeted for
need X
√
X
known not to
support need X
X
√
don’t know
about need X
√
√
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Examples
• <source media=“accessibility(captions:yes)” src=“A”/>
• <source src=“Z”/>
• <source
media=“accessibility(captions:yes audio-description:no)”
src=“A”/>
• <source
media=“accessibility(captions:no audio-description:yes)”
src=“A”/>
• <source src=“Z”/>
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Source Configuration
• If source has ‘optional’ features (e.g. a separate
text overlay stream for captions)
• Let the media engine default enable/disable track
the user preferences [out of scope]
• Let scripts:
– enquire user preference
– enquire source provision (‘is there a caption track?’)
– affect source configuration (‘turn on caption track’)
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PRESENTATION ISSUES
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Who renders captions?
• In media file: media engine
• Handled by script and placed into DOM: web
engine
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Scripted Accessibility
• Enables custom controllers to turn provisions
on/off
• Sync’ing slides, scripted captions etc.
– Cue ranges, where art thou?
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LEVERAGE AND ACTION
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Resources
•
•
•
•
•
SMIL for synchronized media
Media queries for presentation needs
Media engine accessibility provisions
Scripting, the DOM and events
Dublin Core and IMS for user preferences?
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Action?
• HTML:
– revive cue ranges
– describe using media queries to select for
accessibility (informative)
– describe using user preferences to configure for
accessibility (informative)
– Script access to or control of features of the media
• CSS
– Media queries for accessibility
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