It's about a porn star who is at the end of his career but he's got a wife and a young son. This shady bloke comes up to him and offers him loads of money to do one more porno. He asks what it's about etc but the bloke says he wants it to be a surprise, filmed like a kind of reality show in this secluded building. After much deliberation he decides to go for it.
It basically turns into a mad murder porno because they keep injecting him with some drug which makes him go sick, and he can barely remember what he's done after. There's paedophilia, necrophilia, rape and new born rape. It never shows any real penetration, so that's probably how it got past whatever censors they have in Serbia. There is an uncut version apparently, but I watched the full version.
I found it difficult to get over it for about 2 weeks, not like nightmares or anything but just a stomach turning horror when I thought about some of the scenes.