Understanding WCAG 2.0

Skip to Content (Press Enter)


Captions (Live):
Understanding SC 1.2.4

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

Intent of this Success Criterion

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.

Specific Benefits of Success Criterion 1.2.4:

  • People who are deaf or have a hearing loss can access the auditory information in the synchronized media content through captions.

Examples of Success Criterion 1.2.4

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques and Failures for Success Criterion 1.2.4 - Captions (Live)

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. G9: Creating captions for live synchronized media AND G93: Providing open (always visible) captions

  2. G9: Creating captions for live synchronized media AND G87: Providing closed captions using any readily available media format that has a video player that supports closed captioning

  3. G9: Creating captions for live synchronized media AND G87: Providing closed captions using one of the following techniques:

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

Additional Techniques (Advisory) for 1.2.4

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.

(none currently documented)

Common Failures for SC 1.2.4

The following are common mistakes that are considered failures of Success Criterion 1.2.4 by the WCAG Working Group.

(No failures currently documented)

Key Terms


the technology of sound reproduction

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


synchronized visual and/or text alternative for both speech and non-speech audio information needed to understand the media content

Note 1: Captions are similar to dialogue-only subtitles except captions convey not only the content of spoken dialogue, but also equivalents for non-dialogue audio information needed to understand the program content, including sound effects, music, laughter, speaker identification and location.

Note 2: Closed Captions are equivalents that can be turned on and off with some players.

Note 3: Open Captions are any captions that cannot be turned off. For example, if the captions are visual equivalent images of text embedded in video.

Note 4: Captions should not obscure or obstruct relevant information in the video.

Note 5: In some countries, captions are called subtitles.

Note 6: Audio descriptions can be, but do not need to be, captioned since they are descriptions of information that is already presented visually.


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

Note 1: A broadcast delay is a short (usually automated) delay, for example used in order to give the broadcaster time to queue or censor the audio (or video) feed, but not sufficient to allow significant editing.

Note 2: 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