I aasked this a few days ago and thought it was a simple question - apparently not. 

Got comments in Studio U that this is a legal question, then it was a copyright question - neither is correct. I did finally go to Trust& Safety who also had  difficulty understanding the question.

Then finally after several communications they said to put the credits at the end of a course. When I asked what that ment - they could not explain it. 

They have now agreed that they can be added at the end of the video which uses the material, just like the credits you see at the end of a TV show. 

There is lots of free material on line, but much of it, under creative content requires that proper attribution be given (who made it - where is the CC license). Don't use material without doing this, and at the end of the video makes sense. 

At the end of the course makes no sense.