Audio descriptions should be provided for non-live video.
Audio description (AD) is defined as “the verbal depiction of key visual elements in media and live productions.” Essentially, AD is a narration of meaningful visual information in a video to provide context, clarify speakers and articulate visual elements.
This video from Rooted in Rights provides a quick introduction to audio description.
AD is important for individuals who are blind or have low vision. It is key to revealing detailed information that sighted people consume without a thought.
The following trailer from the movie Frozen is a good example of how audio descriptions can be incorporated into the main audio track of a video.