A.2 WCAG 2.0 Success Criterion 1.2.7 − Extended Audio Description (Prerecorded)

If the content of a video is complex, the audio within the video may not effectively explain what is taking place in the visual. Some visually impaired persons listening to the audio will miss out on important content. To rectify this, provide an extended audio description which describes in detail what is taking place in the visual. Often in these cases the visual may need to pause while the audio description plays.

An extended audio description may state things like "The person is now doing X in the video.  Now the person is doing Y."

Before Rectification

In the example above, there is a risk that a user has not enough time to understand all the information before the video moves onto the next point because they cannot see the visual.

After Rectification

This example shows how the system can handle this by temporarily pausing the video and providing audio to explain the situation.

WCAG 2.1 Reference:

https://www.w3.org/WAI/WCAG21/Understanding/media-alternative-prerecorded