Possible Duplicate:
Detecting if youtube is blocked by company / ISP
Is there a way to test if a user's browser has access to YouTube servers using JavaScript or PHP?
Some companies block access to certain sites, like YouTube for obvious reasons, and therefore it's necessary to stream fallback videos from a different CDN if that is the case. I currently have a solution using ActionScript, but I would prefer to use PHP or JavaScript to replace the div instead if that's possible.