Go to youtube and find your video
copy the url of the video

Use full reply mode here
Select the 'insert media tag' icon at the top ( next to the 'insert image' icon)
Pick 'youtube video'
Paste in your video's url when the box opens up

Submit reply
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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