After your fresh install phpBB forum, usually users can not post their video link such as YouTube to the forum. It's because the permission is default set NOT to allow it. The only thing you can do is adjust that permission.
Then, whenever you want to embed an Video to the forum. Just follow this code:
[flash=500,300]www.youtube.com/v/XXX&hl=en[/flash]
What you should do next is change the XXX by the code of YouTube video. For example, the http://www.youtube.com/watch?v=Jb9TpZSJJa0 have the Jb9TpZSJJa0 code.
Have fun!
Then, whenever you want to embed an Video to the forum. Just follow this code:
[flash=500,300]www.youtube.com/v/XXX&hl=en[/flash]
What you should do next is change the XXX by the code of YouTube video. For example, the http://www.youtube.com/watch?v=Jb9TpZSJJa0 have the Jb9TpZSJJa0 code.
Have fun!