Ok, I've been looking everywhere for the answer to this. When I use the embed code from a youtube clip and put into my Sharepoint 2010 Blog post (using the HTML source option), it shows up just fine in the preview (along with a warning that some of the code may be changed). But then when I publish my blog the video disappears and when I go into edit mode I find that the embedding code has been stripped away.
Please can someone tell me how to stop sharepoint from doing this. The only lead i have that looked hopeful was a post that said this was possible to turn this behaviour off (although not desirable) but then they didnt say how to do it.