This requires youtube-dl to be already installed in you system and present in your path.

You can install it using

sudo apt-get install youtube-dl


brew install youtube-dl

Then just adding the following lines in your bashrc or zshrc file will enable you to download music from any youtube video, just by typing `dym`

alias dym='youtube-dl -f "bestaudio[ext=m4a]" --embed-thumbnail --add-metadata

You can play around and tweak the flags according to your needs.