• Success Criterion 1.2.4
  • Conformance level AA

Live Captions So Delayed They’re Useless During the Event

1.2.4 — Captions (Live)

Scenario

Setting

A car-rental site's checkout flow

What’s wrong

Live captions with latency so severe they can't be followed against visuals/slides.

Example 

<div class="live-support-call">
  <video src="live://support-agent-feed" autoplay></video>
  <div class="live-captions" id="cc-box"></div>
</div>
<!-- Captions arrive 15-20 seconds after the audio, long after the
     agent has already moved on to a different point on screen -->

Why it matters

A deaf customer on a live support call reads what the agent said 15 seconds ago while the agent has already scrolled three screens ahead, making the captions useless.

How to test

Watch live captions against the speaker/slides: if the lag makes them unreadable relative to what's currently being shown, it fails.

How to fix

Live captions need latency low enough to track the video in real time; anything beyond a few seconds breaks comprehension for fast-moving visuals.

<div class="live-support-call">
  <video src="live://support-agent-feed" autoplay></video>
  <div class="live-captions" id="cc-box"></div>
</div>
<!-- Switched to a low-latency captioning provider (under 3-5 seconds)
     and reduced encoder buffering on the live stream -->

Outcome

A deaf customer follows the agent's screen-share step by step without falling behind.

Who is affected

Deaf and hard-of-hearing customers on live support calls lose the ability to follow real-time instructions when caption latency runs into double-digit seconds.

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