But my old videos are still only showing as previous a tall back box ??
I still have the style sheet extras.
Since you basically "added a new UBBCode" (or updated your current code), you need to run the content rebuilder.
Control Panel » Content Rebuilder > Rebuild Posts
Rebuild Posts
Select this action if you've added a new UBBCode or if you've edited the list of censored words.
hint: If you enter the post editor on one of your old youtube posts and click the "Preview Post" button, you will get an idea of what the rest of your posts will look like before running the rebuilder on your whole forums.