Understanding WCAG 2.0

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Captions (Live):
Understanding SC 1.2.4

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1.2.4 Captions (Live): Captions are provided for [begin add]all[end add] live [begin add]audio content in[end add] synchronized media. (Level AA)

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Note: If synchronized media is completely computer generated, it is not live and is subject to the requirements for prerecorded synchronized media[begin delete] in WCAG 2.0 [2457] [end delete].

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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.

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. The techniques listed only satisfy the Success Criterion if all of the WCAG 2.0 conformance requirements have been met.

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 [2393]

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


[begin add]synchronized visual or text equivalent for both dialog and non-dialog audio information needed to understand the media content[end add][begin delete]text presented and synchronized with synchronized media to provide not only the speech, but also non-speech information conveyed through sound, including meaningful sound effects and identification of speakers [end delete] [2561] [2518]

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

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

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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.

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

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

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

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Note 7: In some countries, the term "subtitle" is used to refer to dialogue only and "captions" is used as the term for dialogue plus sounds and speaker identification. In other countries, subtitle (or its translation) is used to refer to both.

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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[begin add], unless the media is a media alternative for text that is clearly labeled as such[end add] [2393]