Linux: youtube-dl

Youtubedl

Debian instalation:

       sudo curl https://yt-dl.org/downloads/2014.04.04.7/youtube-dl -o /usr/local/bin/youtube-dl
       sudo chmod a+x /usr/local/bin/youtube-dl

Ussage:

       youtube-dl <URL>
       youtube-dl --max-quality=mp4 http://www.youtube.com/NOMBREdeVIDEO
       youtube-dl --extract-audio --audio-format mp3 https://www.youtube.com/watch?v=6NsGQ2liIkk
       youtube-dl --extract-audio --audio-format mp3 --audio-quality 0 -o "./Summer Music Mix 2018.mp3" https://www.youtube.com/watch?v=Ur_tXqaNXOI  # 0 best, 9 worst

ffmpeg install

https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu

cd Desktop
-/Desktop# git clone git://source.ffmpeg.org/ffmpeg.git ffmpeg

after clonig complete 
-/Desktop# cd ffmpeg

afte that configure it by typing 
-/Desktop/ffmpeg#./configure

lastly execute following command on terminal
~/Desktop/ffmpeg#sudo make && sudo make install