Toribash
You need to upload it to YouTube
and then you take the link.
This is how you do it, for example, for this link
http://www.youtube.com/watch?v=yQOdiTny2Vk
You take the yQOdiTny2Vk, and the put it in the bbcode like this.
[YOUTUBE]yQOdiTny2Vk[/YOUTUBE]
For spoiler it should be like
[SPOILER="This"][YOUTUBE]yQOdiTny2Vk[/YOUTUBE][/SPOILER]