If you think about it, if they leave your site to go to Youtube, and you still have control of their browser to force them back after the video has ended, you’ve basically created a virus. Once they’ve left your site, you lose control. You can’t tell youtube what to do.
That said, you could, of course, simply embed the youtube video on your site so that they watch it without leaving,
or you could use an iframe to imitate them leaving your site for youtube while they actually stay on it. You wouldn’t be able to truly have it redirect once the video ends, but you could set a timer for redirection that is the same as the length of the video.
But really, what are the chances that someone is going to visit your site, click the link to the youtube video, sit and watch it for the full length, and then be glad that they’re automatically forced back to your site?
