Provide live text for live audio-only content
G150 covers giving live audio-only content a text alternative while it is happening, through real-time stenography, rapid typing, or re-voicing into speech recognition trained on one operator. W3C is candid that this is the hard case. There is no time to correct a mistake, no chance to listen again, and no room to paraphrase when the words are arriving quickly. W3C lists it as sufficient for 1.2.9 Audio-only (Live), which is Level AAA. That is worth reading twice, because the Level A rule with a similar name covers prerecorded audio and video only, and by its own definition excludes live content. So this is a genuine accommodation and it is not part of a Level AA claim.
How we find it in an audit
No scan reaches live content. Our reviewers watch a live event as it happens, checking that a text version exists during the broadcast rather than after it, that it keeps pace with the speech, and that it names the speakers. A transcript published the following day is a different technique answering a different rule.
How affected users experience it
A public hearing streamed as live audio with no text is closed to deaf and hard of hearing residents while the decisions are being made. A transcript a week later is not the same event. The chance to submit, to object, or to call in has gone. Real-time text is what makes the meeting attendable rather than merely reviewable.
Passes vs. fails
Passes
A live captioner feeds real-time text beside the stream, so deaf listeners follow the hearing while it is going on.
Fails
A council streams live audio of its public hearings with no text version while the meeting is happening.
Other ways to satisfy this rule
3 guides on this site are filed under 1.2.9 Audio-only (Live). W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
This guide is our interpretation of W3C technique G150: Providing text based alternatives for live audio-only content. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.