that is THE question these days! Thousands of users watch youtube content online every day, but especially if you are on a slow modem line and downloaded a large clip you don't want to do this over and over again. So many ask for the steps to save YouTube video. There are numerous descriptions, tutorials and help texts out there:
number 1 - How To Save Flash Videos From YouTube number 2 - YouTube videos to iPod or PSP? number 3 - How To Download And Save Youtube Videos number 4 - Greasemonkeying with Google Video and YouTube number 5 - Youtube Videos lokal speichern (german) number 6 - YouTube speichern und FLV abspielen (german)
And some services specialising in helping you to track down the video file and save it to your disk. www.Keepvid.com is the oldest and most known site, but there are also www.fileleecher.com javimoya.com and a lot more (try google)
Another thing are installable scripts and helper applications like the videodownloader 1.0 for Firefox which enables you to download embedded videos and media files with your browser from Youtube, Google, Metacafe, iFilm, and over 60 other video sites.
The basic principle behind all these is tracking down the location of the real .flv (flash video) file and downloading it to your computer. You can then play the file as often as you like with a flash video player.
Once, in the YouTube case, you had to get the id of the video you'd like to download and append it to this URL: http://www.youtube.com/get_video?video_id=******* Your browser would then promt you to download a file with a .html extension. Rename this to .flv and tataa, that's it.
But YouTube changed its backend to make things a bit harder. Now you have to peek at the sourcecode of the page. Go to a line that looks like this and var fo = new SWFObject("/player2.swf?video_id=(copy this part)", "movie_player", "450", "370", 7, "#FFFFFF"); (also, see this image) This should be the real source of the file along with dynamic session variable data.
We will see what is next...