To embed video to play in a thread:
1) take the URL from the address bar and highlight all text after the = sign.
2) ctrl-c to copy and ctrl-v to paste it into the body of your message in the thread.
3) put [ YOUTUBE ] on the front of what you pasted in, and [ /YOUTUBE ] on the end of it. (remove the spaces between the word "youtube" and the brackets)
4) Bam! You're done.