The app WallpaperEngine can somehow set the Wallpaper to a HTML page, scene or video. I'm trying to do pretty much the same thing, so I looked and found this option in VLC to set a video as a wallpaper:
But that just creates a window and not an actual wallpaper. You can see this in the Desktop switcher:
The WallpaperEngine background (the purple one with the pink blob in the screenshot that you can see on Desktop 2 and 3 and in the background) behaves like a regular wallpaper (but animated). How do they achieve this? Is there some hidden API that allows setting a video stream as a wallpaper or do they just set the wallpaper to that every few milliseconds?