An ECU (extreme close-up) fills the frame with just one part of the face — eyes, mouth. A CU (close-up) takes the whole face, an MS (medium shot) goes waist-up, and a WS (wide shot) shows the full body plus the space around it. That progression is both how close the camera physically gets and how close the audience is meant to feel.
The same line of dialogue carries different emotional weight depending on the shot size — an ECU amplifies the smallest flicker of expression for tension, while a WS treats the person as one element within an environment, building distance or isolation. Editors typically open a scene wide to establish space, then cut progressively closer through MS and CU.
The white frame in the demo carries corner brackets like a real viewfinder. Narrowing or widening just that frame around the same figure is enough to move between all four sizes.
When to use
When storyboarding or building a shot list, decide the intended emotional distance first, then pick the size. Switching too often within one scene breaks the rhythm.