If you don't consider it too much of a pain, I tried downloading a YouTube "Official" movie trailer, without ads and copying it to the same folder as my movie using the instructions below with the same file naming convention as the .XML file and with *.trailer.* in the name (full Mede8er's instructions below) and it works flawlessly without any changes being made to the XML file. I don't use the JukeBox+ feature yet so I can;'t speak to that but it does work for my Favorites page. It doesn't matter what format you use either, MP4, MKV, whatever. The Mede8er just sees it and puts it up on the movie information page and plays it. It would however be nice to have a tool to batch this process but I don't see that coming anytime soon. It will add another 35-50 MBs to each folder, so it'll eat up a little more space on your drive but that's expected if you want your trailers stored locally. I think it's pretty cool, just a pain and a lot of time spent in my future to do that for each of my 100s of movies.
"Instructions:
Copy Movie Trailers into Movie Folders
Name the Movie Trailers 'xxxxx.trailer.*' xxxxxx = any name * = extension
If X3D finds the local trailer it will play it from Trailer Play Icon on the info sheet (about.jpg) and if not it will play the YouTube Trailer as normal if the xml has the <Videos> node.
Instructions for JukeBox+
As above but copy the trailers into the movie folders in the 'data' folder of the JukeBox+"Have fun,
~ Larry