Go to youtube and find your video
Copy the url

Use the full reply mode here
Click the 'enter media tag' icon - it's next to the 'enter image' icon
Select 'youtube video' from the list
Paste the url of your vid into the box that pops up

Submit reply

Presto!
_________________________
She was standin' alone over by the juke box, like she'd something to sell.
I said "baby, what's the goin' price?" She told me to go to hell.

Bon Scott - Shot Down in Flames