...I think if you have a proper Mac computer it is possible using something called Handbrake Lite, but I have never managed to get this to work.
(this should be free, too. If you find a site trying to charge you for it, it is a con)
...I have a Mac with Windows installed as a parallel system, so download You Tube stuff in Videora then drag and drop into the Mac OS.
I confess that this is a bit fiddly and Geek-tastic even for me...