Find Videos Inside a Post

This is the statement I am currently using to extract YouTube URLs from a post:

preg_match('|http://www.youtube.com/watch\?v=([a-zA-Z0-9\-\_]+)|', $post->post_content, $matches);

$matches[1] contains the ID of the first video. This may not cover all the YouTube URL formats, but it should give you a start.