Hi, hopefully this is a simple question. I have a simple custom forum on my site written in PHP. For security reasons I don't allow any HTML in the forum posts. I only allow certain BBCode tags. I would however like to allow embedded YouTube videos.

So my question is this: What's the best (most secure) way to validate the YouTube embed code? YouTube is currently using iframes to embed videos, but obviously I can't just allow the iframe tag. I also need to ensure the src of the iframe is a YouTube URL, and ensure there's no other malicious bits of code in the iframe code.