1.2.3 Audio Description or Media Alternative (Prerecorded)
Provide alternatives for time-based media.

About

Providing audio description of the video content enables people who are blind or visually impaired to access the visual information in the presentation.

Example:

Before Rectification

video image without transcript.

With video as this one; people with visually difficulties will be able to hear the audio but will not be able to see the picture.

After Rectification

video image with transcript.