A.1 WCAG 2.1 Success Criterion 1.2.6 Sign Language (Prerecorded)
Sign language is a method universally used by people beset with hearing impairment to access audio content. This provides the ability to reflect emotion, intonation and other audio information that may be limited when using captions.
Before Rectification
Simply having the video with a transcript or captions may not be enough for all users.
After Rectification
A more reliable method is to translate this information through sign language as is seen in the image above.
WCAG 2.1 Reference:
https://www.w3.org/WAI/WCAG21/Understanding/sign-language-prerecorded