This might be a bit of a stretch for a suggestion but the replayer here at RIO is kinda difficult to use for anyone doing intense studying. Or, maybe it's just those who are doing intense studying with ADD.
Anytime I'm studying--whether at RIO, YouTube, or elsewhere--I often need to rewind the video a few seconds. I do this multiple times throughout any video, often in the same spot. For those tougher concepts, or mumbled words, we really need an easy way to go back and listen/watch.
I know whatever video platform you're using just might not have that capability, and switching is probably impossible. But if that capability is possible I'd love to see it added.