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What you do is you go to the video, and at the end of the link it will have a v= and a bunch of numbers and letters. You copy everything after the v= go into advanced reply, and click the youtube symbol, it will wrap youtube tags around selected text. (select the copied stuff) and the tags wont work if you type them in, they only work if you put the tag around them by clicking the symbol. It will show the vid on your post.