this might be due to YouTube's TOS.
They hold copyright and don't allow downloads without their permission, so I wonder if they are breaking these apps.
I've downloaded two apps for saving YouTube videos but can't get either one to work: KeepTube & YouTube Downloader. The first brings up lots of code in Keynote but does nothing; the second downloaded the two videos I entered the URLs of, but under Status it said Error - without explaining.
What's a simple way to save YouTube videos?