Going through my old linux and macOS cheatsheets, I found this, youtube-dl; it lets you rip youtube vids and download them.

sudo apt-get update && sudo apt-get install youtube-dl
youtube-dl <youtube vid URL>

It's also available on macOS. If you use brew, you can get it with this

brew update
brew install youtube-dl

youtube-dl <youtube vid URL>

I think you can also do this in Windows with Cygwin, but I haven't tried that.

UPDATE:

Rishabh GuptaFollow

I'm a software developer interested in programming language theory, system architecture and security.

added in the comments. Windows users can also get this via a Python package. You can get the EXE from rg3/youtube-dl