Note that prerecorded audio-only and prerecorded video-only files are covered here. Live-audio-only and Live-video-only files are covered below (see 3rd paragraph following this one).
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Non-text content that is time-based media is made accessible through 1.2: Time-Based Media. However, it is important that users know what it is when they encounter it on a page so they can decide what action if any they want to take with it. A text alternative that describes the time-based media and/or gives its title is therefore provided.
For Live Audio-only and live video-only content , it can be much more difficult to provide text alternatives that provide equivalent information as live audio-only and live video-only content. For these types of non-text content, text alternatives provide a descriptive label.
https://www.w3.org/WAI/WCAG21/Understanding/non-text-content.html :
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