- 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.
Learn more
- Understanding Understanding document (opens in a new tab)
Related scenarios
- Live Event Streamed With No Captioning Plan at All
- Live Webinar Audio With No Real-Time Captions
- Live Caption Feed Separated From the Video Player
- Live Captions That Cut Out Partway Through the Event
- Live Auto-Captions Too Inaccurate for Technical Content
- Live Captions Unreadable Due to Overlap or Low Contrast