However, the bit that really concerns me is the 'nasty' bit. I watched a few seconds of the video and at times the girl looks like she is crying and in pain.
Yes, it is concerning & she probably was. I'd put money on her emotions being genuine rather than worthy of an Oscar.
That industry isn't as well regulated as we'd hope.
The women are often scouted in the sex industry, strip clubs, prostitution.
There are contract "stars" who work in a more regulated environment with an established production company. It'll be cleaner, they'll get tested & only do what they've agreed they will be comfortable with. Then there's the rest. Plus, if it's another country it's even harder to determine what conditions these people are working in.
There was a director who was considered well known & served jail time because he violated laws. Allegedly there were 2 versions of this film & the one released in Europe was way worse but wasn't used against him. After filming he records a sort of exit meeting with the girls as proof that they're happy with what has taken place & he's very nice, but it's clear that they're shaken up & frightened. Once it's started they're not in a position to stop it.
I would find it alarming OP. To see another person hurt is normally very difficult, to enjoy it sexually is depraved.