When using videos for educational purposes, they need to have audio descriptions. What are audio descriptions? They are a spoken, verbal explanation of what is occurring in the video. The audio descriptions are captioned, as well.
For an example, take 3 minutes to watch these two, almost identical 1.5 minute videos. Close your eyes and listen to the first video. Do the same thing and listen to the second video. The first video probably made much less sense than the second, and hopefully illustrates the use and value of audio descriptions.