How to extract audio from youtube videos

The general idea is 

1. Download the video file to your computer. (This file contains images and the audio which combined represent the video you are seeing).
2. Use some kind of extraction tool to save the audio track.

Lets do it now on Windows:

Windows

1. Install a Firefox extension called "DownloadHelper". The extension web page is currently broken but the download link still works: https://addons.mozilla.org/en-US/firefox/downloads/latest/3006/addon-3006-latest.xpi
2. Using firefox browse to the youtube video page which audio track you are interested in.
3. Click the Icon named "Download Helper" > {your video name} > "Quick Download", as show in following image :
   
4. Using windows explorer open to the folder to which the FLV file was downloaded (the FLV file is the file contains the video record). You can find this folder quickly by clicking in Firefox
1. Tools > Downloads to display the downloaded files window
2. Right click on the file you just downloaded 
3. Selecting "Open Containing Folder"

Now to the tool which will allow you to extract the audio tack

1. Download a little utility called FLV Extract from here http://www.moitah.net/download/latest/FLV_Extract.zip
2. Open the downloaded zip file, in which you will find a file called FLVExtract (Virus free, if unsure use virustotal.com to scan before launching the application).
3. Drag the file from the folder to which you downloaded the file into the FLV Extract windows

Done! In the same folder you now have 3 files: 

• {your video name}.avi, 
• {your video name}.mp3, 
• {your video name}.txt

{your video name}.mp3 is the file you are interested in! This is the audio of your loved video.

Hope you find this useful,

Maxim.

* p.s. 

If you are interested in mp4 audio extractions, Linux, Mac or in fact any other combination of Format, Tool & OS let me and I'll extend this post. Thank you, Maxim.