Timed Media Accessibility: Surveying the terrain

David Singer, with help from the web media teamApple 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

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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