The term, Act, in Theatre by contrast to Cinema, has rather a different meaning in regards to content. In this case, and Act is a closed section of the total action of a work.
In Film the term Act is used as more of a technical connection: the finished Film is for example shipped to movie theaters in separate Act containers. The projectionist splices the five to six Acts (approx. 100 to 120 minute film duration) together to form a complete movie.