Understanding Success Criterion 1.2.4: Captions (Live)

Success Criterion 1.2.4 Captions (Live) (Level AA): Captions are provided for all live audio content in synchronized media.


The intent of this Success Criterion is to enable people who are deaf or hard of hearing to watch real-time presentations. Captions provide the part of the content available via the audio track. Captions not only include dialogue, but also identify who is speaking and notate sound effects and other significant audio.

This success criterion was intended to apply to broadcast of synchronized media and is not intended to require that two-way multimedia calls between two or more individuals through web apps must be captioned regardless of the needs of users. Responsibility for providing captions would fall to the content providers (the callers) or the “host” caller, and not the application.



Related Resources

Resources are for information purposes only, no endorsement implied.


Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. However, it is not necessary to use these particular techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.

Sufficient Techniques

  1. Creating captions for live synchronized media AND Providing open captions that are embedded directly in the video stream
  2. Creating captions for live synchronized media AND Providing closed captions using any readily available media format that has a video player that supports closed captioning
  3. Creating captions for live synchronized media AND Providing closed captions using one of the following techniques:

Captions may be generated using real-time text translation service.

Advisory Techniques

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.


The following are common mistakes that are considered failures of this Success Criterion by the WCAG Working Group.

Key Terms


the technology of sound reproduction

Audio can be created synthetically (including speech synthesis), recorded from real world sounds, or both.


information captured from a real-world event and transmitted to the receiver with no more than a broadcast delay

A broadcast delay is a short (usually automated) delay, for example used in order to give the broadcaster time to cue or censor the audio (or video) feed, but not sufficient to allow significant editing.

If information is completely computer generated, it is not live.

synchronized media

audio or video synchronized with another format for presenting information and/or with time-based interactive components, unless the media is a media alternative for text that is clearly labeled as such