8.4 WCAG 2.1 Success Criterion 1.2.3 − Audio Description or Media Alternative (Prerecorded)
When a video with audio is uploaded onto a website, a visually impaired person will be able to hear the audio but will not be able to see the picture. As a result he/she will only have access to part of the information. Websites should either provide additional audio that explains what is happening in the picture or provide a text transcript that explains both the audio and what is taking place in the picture.
Before Rectification
With video as shown in the example above, a visually impaired person will be able to hear the audio but will not be able to see the picture. He/she needs some other ways to know that there is a picture of a person on this screen.
After Rectification
A simple solution to this is to provide a text version that includes dialogue and also explains what is appearing on the screen.
WCAG 2.1 Reference:
https://www.w3.org/WAI/WCAG21/Understanding/audio-description-or-media-alternative-prerecorded