WCAG 2.1 - SC 1.2.2 Captions (Prerecorded)

In video presentations with a synchronized audio component, provide captions describing the audio part of the presentation for hearing impaired viewers.

Official Requirements:

1.2.2 Captions (Prerecorded): Captions are provided for all prerecorded audio content in synchronized media, except when the media is a media alternative for text and is clearly labeled as such. 

How to fix:

If you provide a video with sound, provide captions for hearing impaired people. The captions should include both speech and any other sounds that provide significant information. For example, if your video includes the sound of a squeaky door opening ominously, indicating that something is about to happen, that should be included in the caption.