The tool that can be used for the purpose is Elltube.
To install Elltube open up a terminal and run the command:
The above command will open up the full-blown Synaptic tool. Search for “lame” (no quotes). Scroll down until you see the “ubuntu-restricted-extras”. Mark “ubuntu-restricted-extras” for installation.
Search for “ffmpeg” (no quotes). Mark “ffmpeg” for installation.
Click Apply to install.
Once all of this has installed download the Elltube.deb file and save it to your machine. Then run the command,
sudo dpkg -i /path/elltube_0.3-1_all.deb
This will install Elltube. You are ready to convert videos now!…
You will find Elltube in your Internet sub-menu of either your Main or Applications menu. When the Elltube application opens you will see the Main window.
The first thing you need to do is find a video you want to convert on Youtube. Find the URl and then copy and paste into the Youtube URL area. When you do this the details of the file will appear in the main window. Now what you have to do is to select MP3 (audio only) from the Format drop-down and select a Save to location for the download and conversion. When the details are done, click the Download button and the process will begin.
When the conversion process is complete, the “Video found!” message will change to indicate that the process is finished. When it has completed save the mp3 file to your machine.