I have the option “Include Cinema Trailers from new and upcoming movies in theaters” checked on my server and I the option "Include Cinema Trailers from movies in my library " uncheckd. My goal is watching to new movie trailers only.
It does work, the problem is that Plex is apparently downloading the trailer and then transcoding it and for this reason trailers Never play smoothly and the resolution is terrible. I think Plex could just play a trailer from Youtube because they have cache around the world and the quality is way better.
So basically Plex would just tell the player what url it should play. This eliminates transcoding and uploading from the server. Win-Wiin