Theatre and film are intimately linked mediums of artistic expression. They use many of the same core ingredients (visual, sound and dialogue, time, performance) and even employ most of the same optional conventions (experienced in a single sitting lasting a couple hours, uses non-diegetic music, usually presents the action in its own space and told in roughly real-time for most or all scenes, etc.). Obviously there are exceptions where one medium is used to do something quite different, such as documentary for film or an interactive murder mystery dinner theatre for the stage. But they are closely related media, with film arguably descended directly from theatre. Early film even copied most of theatre's conventions, such as all the action taking place on a "stage" viewed from a single, fixed camera angle straight-on, as though the screen at the movies was meant to be used as an illusion to replicate the "stage" that the audience was used to sitting in front of.
This clip is from King John, filmed in 1899. When movies were new, one of the first things they did with it is adapt Shakespeare, naturally. But as with all art, eventually film went on to discover its own strengths, doing things that you can't do with theatre.
