You only need to post the URL from JTV or Youtube - you don't need the full embed code.
Videos don't always embed in the Preview, but once you've Posted, they'll be there.
For example, if you type
http://juggling.tv/4039
(without using the Code tags) then it will show up like this:
http://juggling.tv/4039
And for youtube:
http://www.youtube.com/watch?v=ACFsn-RwcfM
will show up as:
Kendama DVD extract - Teaser (http://www.youtube.com/watch?v=ACFsn-RwcfM#ws)
For vimeo, same thing:
https://vimeo.com/30959401
...lets you count yourself in:
https://vimeo.com/30959401
Some other video sites will work too. Try it and see....
Wow thats pretty cool! Ive never come across that before.
Added a workaround for the Vimeo embed problem. (See above)