Whenever clips are used, always provide a text alternative! I took one class where the instructor was pretty techno-savvy and made audio clips regularly. She would create the recordings off the top of her head based on discussions in the classroom and events going on around the world. I asked for transcripts of her recordings, but she said the clips were not an essential part of the course as they did not mention things we had to do for the class; instead, they were added just to motivate students and give the otherwise "boring" text classroom a voice. I never did get transcripts, so I never knew what was being said. What if a "normal" student's computer speakers are broken, or if you have a student whose native language is not English? Text alternatives help those people as well.
Some instructors also set up telephone conference calls so students can talk with each other as well as the instructor. I can't participate in these at all, so again, these calls should not be mandatory. But someone (either a student or the instructor) should post "minutes" of the call to the classroom within 24 hours so those who were unable to attend (due to a hearing disability like mine or some other reason such as a different time zone) are not left out.