Adding audio descriptions is pretty much what it sounds like. It's simply using spoken audio to describe what's happening in your video content. For example, things to be included in the descriptions would be:
This description would appear in a separate audio file with optional playback supported by the video.
If you're experiencing déjà vu from the article covering audio and video descriptions in video, you aren't going crazy.
"But why would there be two compliance items that are so similar?"
In WCAG 1.2.3, you can either do audio or text descriptions to accompany the video, and you'll be Level A compliant. To be Level AA, you *must* do the spoken/ audio version description.
Listening is better than describing, so let's cut to the chase. What's a solid example of audio descriptions? Let's look at a clip of The Lion King. You'll notice a few things: