In the old days of Cathode Ray Tube (CRT) displays, a screensaver was literally used to save your screen. That is a motion picture to prevent still image ‘burning into your screen and creating a ghostly permanent image.’
All computers, whether Mac or PC had screensavers, and back then you really couldn’t afford to use one. Lest the ‘permanent ghostly image’ forces you to replace your CRT display. In the old days, you had the option of using pictures as screensavers. They will keep changing after a given time interval to avoid any single (still image) picture from ‘burning into the screen.’
How to use a Video as Screensaver on Mac
Before we go any further, you need to understand that Apple has not made it possible for users to use videos as a screensaver. Though you can have a video as a screensaver using third-party applications, like the SaveHollywood.
Download that application from this link, and install it on your Mac. During the installation process, you will be asked if you want to avail the application to all users or just the current user (you). Select accordingly and click on Install.
After installing the application, you can use any of your favorite videos as your screensaver.
Related: Why do Computer OS still have the Screensavers, yet they haven’t been useful for Decades