Here goes a simple tip on how to extract the audio of youtube videos if you use a linux box.

You will need ffmpeg to be able to proceed with these steps. If you don't have it and are on a Debian descendant box, simply type:

sudo apt-get install ffmpeg

1) Find the video on Youtube

2) Save the video file. There are a couple of options to do it but I am pretty old-school so I do it the hard way:

2a) Clean your browser's cache (if using firefox, simple press Ctrl+Shift+Del and choose "Clear Private Data"

2b) Refresh the youtube page where your video is. This will ensure that your browser re-download your video. Wait until the video has been fully downloaded.

2c) Find the biggest file on your cache (the cache folder is normally on /home/user/.mozilla/firefox/{some code}/Cache) and copy it to something simpler to deal with. An example:

cp 11D49E9Cd01 movie.flv

3) Use ffmpeg to extract the audio as an MP3 from the video file:

ffmpeg -i movie.flv -ab 128k -acodec libmp3lame movie.mp3

The file movie.mp3 will be generated and ready to be played.