This looks like a lot of work.
There are two ways I use to download videos from YouTube.
1. Go to
www.keepvid.com and paste the video URL there. Keepvid will return URLs for downloading the video in different available formats and sizes.
2. Using Firefox, install the Video Download Helper plug-in (there are actually quite a few similar plug-ins for Firefox) Download Helper will put a little icon in one of the browser's toolbars that will let you download the currently-running video. After beginning the download, you can leave the YouTube site, but keep Firefox running, and the download will still proceed. Some sites seem to require that you move to another page before download will start.
I often download videos from YouTube and from other sites that may have streaming media, and have found Download Helper to be very useful. It doesn't always work for all streaming media on all sites, but the developers seem to work at keeping it compatible with YouTube.
