Audio descriptions provide visually impaired viewers with visual context of what is being presented in a video. These descriptions will be read out loud during the video’s playback. Writing good audio descriptions is an art, so learning more about audio description is a valuable starting point. See Turning Sights into Sounds: The Art of Audio Descriptions and Description of Visual Information. There are also vendors who provide audio descriptions, but they are quite expensive and often do not have enough knowledge of the subject matter to create meaningful descriptions. See How to Add Audio Descriptions in Panopto.