Level AA · WCAG 2.0
1.2.4 Captions (Live)
Live video with sound — a webinar, a keynote, a broadcast — needs captions while it is live, not only in the recording published afterwards.
Partly automated Some failures are detectable, others need judgement.
How it fails in practice
A product launch streamed to thousands with captions promised “in the replay next week”. An automatic live caption track that drops names, numbers and every other sentence, and nobody watching it.
How to fix it
Book a live captioner (CART) for anything that matters, or run automatic captions with a person correcting them as they go. Carry the captions in the stream itself, so every player that shows the video can show them.
At a glance
- Level
- Level AA — the level EN 301 549 requires, and therefore the level the BFSG and the EAA are measured against.
- Principle
- Perceivable
- Guideline
- 1.2 Time-based Media
- Added in
- WCAG 2.0
- EN 301 549
- 9.1.2.4
- Automated check
- Partly automated
How to test it by hand
- Join a live stream — or the next scheduled one — and look for a captions control on the live player, not on the recording.
- Watch five minutes with the sound off. The captions keep pace with the speech, name who is speaking when that changes, and include the sounds that matter.
- Check the hard words: product names, people’s names and numbers. They are what automatic captions get wrong and what carries the meaning.
- Ask how captions are produced for the next event. “The platform does it” with nobody checking is the answer that fails.
In code
#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720
keynote-720p.m3u8#EXTM3U
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",LANGUAGE="en",NAME="English (live captions)",DEFAULT=YES,AUTOSELECT=YES,URI="captions-en.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720,SUBTITLES="subs"
keynote-720p.m3u8Partly automated
How far an automated check gets
A tool finds some failures here and cannot see the rest. A clean automated result means the checks that exist found nothing — not that the criterion is met. This is the gap that makes a green scan look like an accessible site, and it is where the keyboard agent, the agents still in development and a human reviewer do the remaining work.
Related criteria
Other criteria under the same guideline.
Further reading
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Captions
Synchronised text for speech and meaningful sound in video; required for prerecorded (WCAG 1.2.2, A) and live content (1.2.4, AA).
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