WCAG 2.1 Criteria Documentation

1.2.4 Captions (Live) – (Level AA)

High-Level Description

Live videos with audio must have real-time captions available for viewers who are deaf or hard of hearing. This ensures equitable access to spoken dialogue, sound effects, and speaker identification during live broadcasts, webinars, meetings, events, or news streams. This supports real-time communication in a world where virtual meetings and live streaming are an everyday occurrence.

Detailed Description

Applies to:

• Live multimedia content: news, webinars, live-streamed events, broadcasts, public meetings.

Requirements:

• Captions must be:
  • Synchronised in real time
  • Accurate and complete
  • Include non-verbal audio - laughter, applause
  • Available to all users - visible or toggleable

  Delivery Methods:

  • Human captioners - CART services
  • Automated speech recognition (ASR) with human monitoring
  • Captioning APIs integrated into platforms like Zoom, Youtube Live, Microsoft Teams

  Note: Live captions do not need to meet the same level of precision as pre-recorded, but they must be functional and meaningful in real time.

  Indicators of Non-Compliance:

  • No captions provided during a live stream.
  • Captions only available after the event and not during the event.
  • Delayed or out-of-sync captions causing confusion.
  • Automated captions with high error rates and no review.
  • Captions available in a separate window that isn't synchronised or screen- reader friendly.

  Real-World Examples & Scenarios

  Scenario	Example of Good Alt Text or Accessibility Fix	Non-Compliant
  Company Town Hall A CEO hosts a live company-wide video meeting	Captions are enabled through a live CART provider. A deaf employee can follow the entire speech in real time	The meeting has no live captions available. Deaf and hard-of-hearing employees cannot follow the meeting
  News Broadcast A local news station airs a live emergency update	Captions are automatically generated, with an editor correcting key terms in real time to maintain clarity	There are many errors in the captions. Users following the captions lose meaning and clarity of the broadcast
  University Lecture A professor teaches a remote class via Zoom	The platform's live captioning feature is turned on, and students can toggle captions or download them afterward	The remote lecture is started without captions on and there is no control to toggle them on or off

  Disability Impact

  Disability Group	Without Captions	With Captions
  Deaf/Hard of Hearing	Cannot access live spoken content	Real-time understanding of speech and cues
  Deafblind	No access unless alternative format available	Captions can be accessed via braille displays
  Non-native speakers	Difficult to follow fast speech	Captions improve comprehension and retention
  Noisy environments	Missed content due to background noise	Captions enable full access

  Supporting Documentation & Legal References

  • WCAG 2.2 Success Criterion 1.2.4 - Captions (Live)
  • W3C Technique G9 – Providing live captions
  • FCC Captioning Requirements for Broadcasters

  Remediation Strategies with Tools & Code

  1 - Enable Live Captions on Platforms

  • Zoom / Google Meet / MS Teams - most now offer built-in live captioning.
  • Ensure settings are enabled before the event.
  • Always test in advance.

  2 - Use Third-Party Captioning Services

  • Services like CART, AI Media, or StreamText can stream real-time captions into:
    • Webpages
    • Live players
    • Embedded overlays

  3 - Monitor Accuracy

  • Human oversight is essential for critical events.
  • Avoid 100% ASR (automated captions).