This is the gray area, in my opinion. Because some companies/IPs don't care at all. Others are quite strict about taking down anything that they own and haven't given expressed permission for you to use. Youtube is also getting more aggressive about taking down stuff that violates copyright. Other sites, like Vimeo, have been more flexible... at least for now.
What I'd do is put a disclaimer, both in the video itself and in the info section, that details this was done purely as an exercise and isn't any part of the official property/brand/etc. Lots of people do this and I haven't seen someone get in legal trouble. But I have seen folks get in trouble (basically a cease and desist letter) when remaking a fan version of a game - like that fan Chrono Cross project several years back.