Replace YouTube Link with video Player

[admin]

I run a forum and want to automatically replace any link to a YouTube video with a youtube video player. I can't really find anything like this on the ineternet, but I have seen it in Wordpress.

I'm running PHP.

This is what i'm talking about:

<a href="http://en.support.wordpress.com/videos/youtube/" rel="nofollow">http://en.support.wordpress.com/videos/youtube/</a>