hazard perception test

i started revising for theory but im stuck on the hazard perception as i dont know how it works. On practice videos they usually give you 4 hazards in 1 video but im hearing that in the actual test, there's only 1 hazard per video or 2 developing hazards in one video in the actual exam? Are these practise videos simply just made harder with more things to watch out for rather than the actual thing? i'm using the 4 in 1 app btw