Update: This extension now supports video download from megavideo also
Before I posted a way of downloading online videos and here i found one more extention using which you can download videos from youtube with just one click. Right click and save video.
This Firefox extension is called Download Helper.
Once installed ,if you are watching a video you will get a direct link on your toolbar to download it.

Else if you want to download the videos in bulk, select all the videos and right click to download the videos. Once the download is started , you will see a counter on the download helper toolbar which will show the count of the video downloaded.

The other ways to download videos are
1. keepvid.com
2. kissyoutube.com ( by prefixing “kiss” before video url )
Do you know any other easy way to download video online ??I was not able to download video from google videos using this application !! Did anyone else tried it ???
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An option to change the format would have been great…
hope my guess is wrong, anyway, there is another website to introduce for download youtube video : http://www.mydownloadvideo.com
first goto a youtube downloader site like this one: how to download from youtube
enter you the video url there
and download the video
you don’t need to install any software for this