I can not switch on my multimedia for such kind of question in the lessons. Can you give some clue - is it connected with some software, maybe need an upgrade or just with the system settings of my OS, which is Linux by the way?
Try to ask via the "feedback" this type of question; maybe the duolingo team will see this. I have Windows, and I think Duolingo detected my settings and asked what I wanted to use. You can also look in the settings for Duolingo to see if that helps you find your answer.