There are lots of technique uses to download YouTube video and save or convert it to different format. I share you how I download YouTube video to mp4 format using Firefox browser, greasemonkey ads-ons, and script to download video and save as mp4.

How to save YouTube Video As MP4 Format

Using Firefox browser, add on the Greasemonkey. Here is the link for you to click get the add-ons
Ad-ons link: Click Here

Then Install the greasemonkey script that allow video from youtube to be download as mp4
Script Link: Click Here

To get more details instruction visit this blog
http://googlesystem.blogspot.com/2008/04/download-youtube-videos-as-mp4-files.html