MelodyCan YouTubeRipper plug-in for Internet Explorer is an easy to use program to download video files from Youtube site. MelodyCan supports MP4 and AVI as output formats for video conversion. You can select a desired output format and video size in MelodyCan settings by choosing a suitable encoder for video files. Just click on "Rip YouTube File" button on your Internet Explorer toolbar and the selected video will be saved to your PC in a desired format.
http://www.instructables.com/id/Download-save-and-convert-video-from-YouTube/