A product video already has captions. It also shows important on-screen text ("30-day free returns") that nobody says out loud. What does a blind viewer need?

Audio description is an extra narration track. It speaks the important things that are only shown, like on-screen text or actions. WCAG 1.2.5 asks for it at level AA for prerecorded video. A text transcript that includes the visual details can also help.

"Captions cover it" is the tempting wrong answer. Captions turn the sound into text for deaf and hard-of-hearing viewers. They don't help someone who can't see the screen. Subtitles in other languages translate speech and have the same limit.