[Accessibility] Media alternative for time-based content

[hostle83]

Describe the bug

According to WCAG Success Criterion 1.2.3, pre-recorded audio-only and video-only content must be accompanied by media alternatives for the visually impaired or the hearing impaired.

• Prerecorded Audio-only: An alternative for time-based media is provided that presents equivalent information for prerecorded audio-only content. This could be, for example, a link to a text transcript for an audio clip,

• Prerecorded Video-only: Either an alternative for time-based media or an audio track is provided that presents equivalent information for prerecorded video-only content. For example, a silent movie includes an audio track which includes a description of the action in the video.

Expected behavior

To satisfy this success criterion, either the system would need to automatically recognize that content is audio-only/video-only, or the user needs to be asked whether the uploaded content is audio-only/video-only. The software then needs to prompt the user to upload a media alternative.

At Level A in Success Criterion 1.2.3, authors have the choice of providing either an audio description or a full text alternative. If they wish to conform at Level AA, under Success Criterion 1.2.5 authors must provide an audio description - a requirement already met if they chose that alternative for 1.2.3, otherwise an additional requirement. At Level AAA under Success Criterion 1.2.8 they must provide an extended text description.

https://www.w3.org/TR/UNDERSTANDING-WCAG20/media-equiv-audio-desc-only.html