Glossary · Accessibility term
Sign language interpretation
Sign language interpretation is a signed version of spoken content, usually a video track running alongside the main one. WCAG asks for it in one place, rule 1.2.6, at Level AAA, and only for prerecorded audio inside synchronized media. So a podcast with no video sits outside it, and so does anything live, because no criterion at any level asks for signed live content. It matters because sign languages are languages. The standard's own note says true sign languages are independent languages, unrelated to the spoken language of the same country or region. Which is why a signed track serves one audience rather than all deaf viewers, and why written captions are a second language for some of the people watching.
In practice
Sign languages differ by region and country. W3C names American Sign Language, Black American Sign Language, British Sign Language and Auslan as different from each other, and the relationships between them are not all the same, since Gallaudet's own project describes Black ASL as a variety of ASL rather than a separate language. Either way a signed track is a choice of audience before it is anything else. And not everybody who is deaf signs, particularly people who became deaf later in life, which is why signing and captions are both needed rather than being two answers to the same question.
Captions are not a substitute, and W3C gives three reasons rather than one. Written text is often a second language for a signer. Sign language carries intonation and emotion that captions leave out. And people who communicate in sign language are faster in it, while a video runs at its own pace and does not wait for anybody. There is a fourth thing worth knowing about the technology sold instead, because W3C says plainly that avatars simulating sign language interpretation are not good enough to be adequate.
Producing one is a project rather than a setting. You need people who can interpret, a way to record it, and somebody to edit it against the audio or video. W3C's own guidance is that interpretation can be added after the event rather than filmed live. The framing has physical constraints too, because for most sign languages the signing space runs from below the waist to above the head and at least an elbow's width to each side. A small inset in the corner of the frame often cannot hold that.
Why it matters
It is one of the clearest reasons W3C advises against aiming a whole site at Level AAA. Guideline 1.2 alone carries four AAA criteria, and an organisation publishing video every day cannot interpret all of it. W3C says the quiet part itself, that sign language is not required in most web accessibility policies. The surprise is where else it counts. A sign language version is a sufficient technique for the reading level rule, because for some deaf readers a signed version is easier to follow than a written one. Almost nobody knows that route is there.
Why a signed track is never the whole answer
In WebAIM's screen reader survey, 6.8% of respondents reported being deaf or hard of hearing, and 5.3% reported being both deaf and blind. Deafblindness covers a wide range of remaining sight and hearing, so a signed video reaches some of that second group and not others, and nothing tells you which. That is why captions and a descriptive transcript sit alongside a signed track rather than behind it.
Where this shows up on the site
Related terms
- CaptionsCaptions are a synchronized text version of everything you would hear in a video, covering speech and the non-speech sound that matters as well.
- TranscriptA transcript is the text version of audio or video, and two different things go by that one word.
- Level A, AA, AAALevel A, AA and AAA are WCAG's three conformance levels, and they stack.
- DisabilityDisability results from the interaction between a health condition and the world around it.
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