youtube-dl

Home site: http://youtube-dl.org/

Install
sudo curl -L https://yt-dl.org/downloads/latest/youtube-dl -o /usr/local/bin/youtube-dl
sudo chmod a+rx /usr/local/bin/youtube-dl

Show possible formats
youtube-dl --list-formats "http://www.youtube.com/watch?v=-6Wu0Q7x5D0"

youtube-dl -F https://www.youtube.com/watch?v=aU2ucm8vVU8

Download
youtube-dl -v -o file.mp4 -f 248+251 "http://www.youtube.com/watch?v=-6Wu0Q7x5D0"

youtube-dl -v -o file.mp4 -f '(bestvideo+bestaudio/best)' "https://vimeo.com/245581179"

Extract audio

youtube-dl -v -o file.mp4 -x --audio-format mp3 --audio-quality 0 -f 251 https://www.youtube.com/watch?v=aU2ucm8vVU8