youtube-dl is a small command-line program to download videos from YouTube.com and a few more sites.
youtube-dl is as easy as
brew install youtube-dl on OS X.
youtube-dl allows you to download from many online audio/video sharing websites, not just Youtube.
You can use it to download all videos from a playlist, from a channel or simply extracting the audio from a Youtube link.
From a channel:
youtube-dl -citw ytuser:channel_name
From a link/playlist
Listing all available formats:
youtube-dl -F OKbtC223e30
Download a Youtube video as audio
youtube-dl -f bestaudio OKbtC223e30
youtube-dl is included in many distro’s repo but I recommend you to install from the main website for quicker update. The version in the repo is usually very outdated.