Les enfilées (1980)

A young couple, Ariane and Victor are tired of marital caresses and decides to spice up their sex life. They respond to classified ads in erotic magazines. This leads to a series of scenes with sexually eccentric characters. They decide it would be fun to watch each other having sex with other people, and then they expand this to secretly filming the occasions so that they can watch them afterwards.The theme is in fact obsessive, sometimes obsessive voyeurism.