Yeah I mean, not really an enforceable rule, but I think it's just common courtesy. Do unto others as you would have them do unto you, and all. Personally I'd be annoyed if someone posted a video of a game with me without asking, since if I did know in advance, I'd use a completely fresh setup.
It's a pretty unfair disadvantage to your opponent to not know the video will be posted, then use their standard 'first game with a stranger' setup, and have that broadcasted and somewhat ruined. Obviously it is in their power, as some suggest, to make a new setup every time, but I think the number of people that do this is very minimal.
Anyways not attacking you for it or anything - there are certainly others who post without asking, but as far as I recall, almost all of the games I've seen between top players have confirmation before the game. So this courtesy is probably a good thing to emulate on your route to becoming a 1000 ELO player