Has anyone been able to set who can view a private video on YouTube using the API?
The API isn't designed for this, so it's either very difficult or impossible.
You can only share a private video with 25 of your friends, so you have to first be friends with them, then give them access, which means the api would have to do all of these actions and once you hit 25 people you'd have to stop anyway.
You should probably use a different service or make your own if you want private videos.
www.tugsat.tr.gg
I find it a little rude that you are posting a link to an (correct me if im mistaken) turkish website - you cannot expect everybody (especially as this is an english-speaking community)... actually, Ive worked with the YouTube API which is pretty nice and works very smooth with jQuery and Ajax - but as the others have already mentioned there is no built-in feature for that. you could probably find some sort of work-around as you could integrate you own authentication and login capabilites - but obviously that would not prevent your users not to watch the "restricted" video on the original YouTube site...
Well you could try to load the FLV to your own website. Do a login system and use flowplayer to show it.