Understanding WCAG 2.0

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Audio-only (Live):
Understanding SC 1.2.9

1.2.9 Audio-only (Live): An alternative for time-based media that presents equivalent information for live audio-only content is provided. (Level AAA)

Intent of this Success Criterion

The intent of this Success Criterion is to make information conveyed by live audio, such as video conferencing, live speeches and radio Webcasts, accessible through the use of a text alternative. A live text caption service will enable live audio to be accessible to people who are deaf or hard of hearing, or who cannot otherwise hear the audio. Such services use a trained human operator who listens in to what is being said and uses a special keyboard to enter the text with only a small delay. They are able to capture a live event with a high degree of fidelity, and also to insert notes on any non spoken audio which is essential to understanding the event. A transcript is sometimes a possibility if the live audio is following a set script; but a live caption service is preferred because it plays out at the same pace as the audio itself, and can adapt to any deviations from the script that might occur.

Using untrained operators, or providing a transcript which differs markedly from what actually happens would not be considered meeting this Success Criterion.

This success criterion was intended to apply to broadcast of audio and is not intended to require that two-way audio 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.

Examples of Success Criterion 1.2.9

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques and Failures for Success Criterion 1.2.9 - Audio-only (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.

Additional Techniques (Advisory) for 1.2.9

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.

  • Using metadata to associate text transcriptions with audio-only content (future link)

    Example: Providing, in metadata, URI(s) that point to several text transcripts (English, French, Dutch) of an audio file.

Common Failures for SC 1.2.9

The following are common mistakes that are considered failures of Success Criterion 1.2.9 by the WCAG Working Group.

(No failures currently documented)

Key Terms

alternative for time-based media

document including correctly sequenced text descriptions of time-based visual and auditory information and providing a means for achieving the outcomes of any time-based interaction

Note: A screenplay used to create the synchronized media content would meet this definition only if it was corrected to accurately represent the final synchronized media after editing.


a time-based presentation that contains only audio (no video and no interaction)


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.