To download videos off youtube, there are several ways and I have shared many different ways earlier, but this one too is one more easier way to download the youtube video in either flv or in mp4 version. Here are the tips i shared earlier -

Download youtube videos in safari browser
Download youtube videos on chrome browser
Download youtube videos with pwnyoutube
Download youtube videos with various tools

And here is a better and easier way to download the youtube video in any browser, except Internet explorer.
Open a youtube video and while browsing the video paste the following javascript in the address bar -

To download the video in low quality .flv format -

javascript:window.location.href = ‘http://youtube.com/get_video?video_id=’ + swfArgs['video_id'] + “&l=” + swfArgs['l'] + “&sk=” + swfArgs['sk'] + ‘&t=’ + swfArgs['t'];

To download the video in high quality .mp4 format -

javascript:window.location.href = ‘http://youtube.com/get_video?video_id=’ + swfArgs['video_id'] + “&fmt=18″ + “&l=” + swfArgs['l'] + “&sk=” + swfArgs['sk'] + ‘&t=’ + swfArgs['t'];

This directly takes you to the download pop-up box without you needing to visit any 3rd party website for the download. Thanks to SOURCE: unlockforus.blogspot.com for the cool and easy tip for the download of youtube videos.
There are several ways and tools to download the youtube and Google videos, but this one and the Safari tip which i shared earlier were very easy to go with. The tip is useful for the browsers Firefox, Opera, Chrome and Safari