ClipGrab is a GUI application that can be used to download videos from YouTube and other online video sharing websites. ClipGrab can also convert the video into audio format such as MP3. For Ubuntu users, you can install ClipGrab via PPA Repository. Here is the PPA Repository for ClipGrab. This ClipGrab PPA Repository supports Ubuntu 12.04 Precise, Ubuntu 12.10 Quantal Quetzal, and also Ubuntu 14.04 Trusty Tahr and all derivatives.
ClipGrab PPA Repository
sudo add-apt-repository -y ppa:clipgrab-team/ppa
For other PPA Repository, you can navigate to my PPA Repository Collections.