Success Criteria

WCAG 1.2.4 Captions (Live)

Success Criterion 1.2.4 requires captions for all live audio content in synchronized media. It's a Level AA criterion under Guideline 1.2 (Time-based Media) — the live-content counterpart to 1.2.2's prerecorded-content requirement.

Why live content needs its own criterion

Prerecorded captioning (1.2.2) happens after the fact, with time to review and correct errors before publishing. Live captioning has to happen in real time, which is a materially different (and more expensive) production requirement — this is exactly why WCAG separates the two into distinct criteria rather than treating "captions" as one blanket requirement, and why live captioning sits at the stricter AA level rather than the baseline A level.

How live captioning is actually produced

Real-time human stenography (CART — Communication Access Realtime Translation) — a trained stenographer or captioner transcribes speech live, typically the highest-accuracy option and the standard for high-stakes events (legal proceedings, major conferences).

Automatic speech recognition (ASR) — real-time automated captioning built into platforms like Zoom, YouTube Live, and Microsoft Teams. Accuracy has improved significantly but still lags human captioning, especially with technical vocabulary, accents, or multiple overlapping speakers.

Where this shows up in practice

Webinars, livestreamed events, town halls, and live product demos are the most common places this criterion applies. Since live captioning has to be arranged before the event (not fixed afterward like a recording), this is one of the few WCAG criteria that requires planning ahead in a production schedule rather than being addressable as a post-launch fix.

Common questions

What is WCAG 1.2.4?

A Level AA criterion requiring captions for live audio content in synchronized media, such as live webinars, streamed events, and broadcasts.

How are live captions different from prerecorded?

Live captions (1.2.4, AA) are generated in real time during a live event; prerecorded captions (1.2.2, A) are prepared in advance for recorded video.

Do automatic captions satisfy 1.2.4?

They can help, but captions must be accurate enough to convey the content; low-quality auto-captions with frequent errors may not meet the criterion.