Worth mentioning that if you want a free way to do this that does not require running additional software.
All you have to do is have a video you want to use, download one of apple's through settings, go to the location of the downloaded background (I don't remember where that is right now but a quick google search would take care of this), rename your file to the name of apple's file and then replace it.
Mac will act as if this video is the right video and use it without complaints. Until apple starts doing any checksum checks on these files I doubt this method will break anytime soon.
This has been working flawlessly for me for a while now.
This may take some finagling to make sure that your video file is not so large that your Mac can't handle it and that you are using the right format. But it is not hard to do.
I think you will find that if you try to do that, it will actually not work properly. Visiting the lock screen repeatedly will eventually crash the wallpaper extension, producing a black screen. And updating macOS will reset all your wallpapers.
Backdrop uses a more advanced approach that ensures that it works seamlessly across reboots and macOS updates.
seamlessly across reboots and macOS updates
Famous last words.
> Until apple starts doing any checksum checks on these files I doubt this method will break anytime soon.
Watch as this is used for malware persistence through a code execution exploit. Then Apple will start verifying the file content.
.scr files are untrusted for this very reason.
.scr files are untrusted because they're plain PE executables. You don't need to exploit anything to get code execution because all they do is execute code.
If they were just video files, they wouldn't be such a vector for malware.
You still need to priv esc