In plain language
Every prerecorded video with sound needs captions that include all dialogue and important sounds.
Who it affects
Deaf and hard-of-hearing viewers, and anyone watching video without sound.
How to check
Play each video: turn captions on, verify they exist, match the speech, name the speakers, and include important sounds. Worked example — A car-rental site's checkout flow: play the video and listen for music, applause, or sound effects that carry meaning: if the captions don't include a text cue (e.g., '[applause]'), it fails.
Common misconception
A transcript alone does not meet this rule. Captions must be synchronized with the video, not just available as a separate text block to read afterward. Real example: on a hotel booking site's room-selection page, captions exist but leave out some spoken dialogue or important sounds (music, alarms, applause) — deaf users get an incomplete version.