@Dutchess_III You look at where it says “uploaded by” (like here), and in this case, it said BBC. And if you aren’t sure if this is BBC or another user named BBC (which usually doesn’t happen, because BBC would find some way to reclaim that username), you can click on it. Of course, what happens for me is that it tells me how that channel is not available in my country, because BBC isn’t available for countries that aren’t Britain (but often the actual shows are, like in the clip) – but, if it was someone impersonating BBC, they would not make it so that Americans couldn’t see the channel (and I do happen to know that user BBC on YouTube is actually BBC). And if you go here, you can see how PBS has uploaded a documentary of theirs, so again, if it says “uploaded by PBS”, you’re going to be ok.