You could always try clipgrab you can download youtube videos and also select which format you would like it to be in. It has a nice interface also...

ppa:clipgrab-team/ppa (Click here for instructions on using PPAs.)

sudo add-apt-repository ppa:clipgrab-team/ppa && sudo apt-get update && sudo apt-get install clipgrab

by adding this ppa you will get the clipgrab package...you can search for youtube videos via this application and also copy and paste the link to the video into it and it will download the video, also you can select the format you want it in.