In plain language
Prerecorded videos need an audio description track describing important visual-only content.
Who it affects
Blind and low-vision viewers who need spoken descriptions of important visuals.
How to check
Play the video with the described track (or check one exists); confirm on-screen text, actions and scene changes are spoken. Worked example — A project-management tool's task board: click the link to the described version: if it 404s, is region-blocked, or requires different login than the main video, it fails.
Common misconception
People confuse this with 1.2.3. That one lets you choose between audio description OR a text alternative; this one, at Level AA, specifically requires the audio-description track itself. Real example: on a survey tool's question builder, the video has natural pauses in the dialogue but the audio-description track doesn't use them to describe important visuals.