Others will give you a better technical answer but what I always do is just get the title of the vid, put it into the youtube search engine and then cut and paste that URL.
(, Wed 12 Oct 2011, 12:30, Reply)
Copy the address up to the & sign. If it's a youtu.be link, copy that into the address bard of a browser, and it will expand to the correct address i.e youtube.com
youtu.be/2bS_3JAGXS8 in browser address bar turns into http://www.youtube.com/watch?v=2bS_3JAGXS8&feature=youtu.be so only use the text in bold.
(, Wed 12 Oct 2011, 12:37, Reply)
Yes, yes they will.
(, Wed 12 Oct 2011, 12:39, Reply)
(, Wed 12 Oct 2011, 13:42, Reply)