WCAG 2.1 - SC 1.2.3 Audio Description or Media Alternative (Prerecorded)

Provide an alternative for the visual portion of a media presentation for sight impaired users, either by providing an audio description of the prerecorded video content, or by providing a text alternative

Official Requirements:

1.2.3 Audio Description or Media Alternative (Prerecorded): An alternative for time-based media or audio description of the prerecorded video content is provided for synchronized media, except when the media is a media alternative for text and is clearly labeled as such. (Level A)

How to fix:

• One approach is a supplemental audio track, with audible explanation of what's happening on screen, placed during existing pauses in dialog.
• Another approach is to create a text description describing everything going on in the presentation — the dialogue, the setting, the visual context, and all the action.