Before continuing, there is nothing here that should cause issues for you however it is worth noting that this will ramp your CPU usage up a lot, since you’re running a video constantly on your desktop – which could result in negative long term effects.
Starting off, if you don’t already have a video to use for your desktop background, it may be worth looking at the Apple TV screensavers.
Save the video’s somewhere permanent that you’ll remember, for example mine are saved like so /User/Movies/Apple/dubai_night_1.mov
In order to set a video as your screensaver (or background, in this case) – you will need to download and set SaveHollywood as your screensaver with the videos you wish to use.
Then, put the following two scripts in a folder in /Library/Scripts/ – I called the folder Background Video for convenience.
nohup /System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background &
If you haven’t already, you will need to set your Terminal profile to close when Shell exits and set .sh files
You could set this up with a crontab to start automatically with your PC, if that’s your thing.