If you can prove that the person was brake checking, it's their fault in my country. But generally speaking they can just say "I thought I saw a deer" if it's a country road or maybe a cat if it's in the city. So don't follow people very closely.

But if it is indeed the case that they cut you off and then brake check, your video footage will prove it very easily.

Generally you'll get cut off first or the person is already being a nut.