I know the problem u are talking about, the way you can do it is by creating your title and then putting ONLY a smilie in post # 1. (or one or two letters, it doesnt matter)
A second later click "EDIT" Backspace out your smilie, and paste in your embedded code for the youtube Video.
The "paste" of your embedded code will work properly the same way it works in the quick reply box if you follow these instructions.
This is the correct answer.
When you start a thread it starts out in Advanced Mode. When you are in Advanced Mode you can't paste embedded code. When you edit a post it's not in Advanced Mode so you can past embedded code. Note that when you are editing a post there is a button that allows you to switch to Advanced Mode in case you want to choose smilies which is available in that mode.