I get my trailers from using Media Center Master. It will automatically download my trailers for me. I generally only do a trailer grab once every 3 months or so, so it's not like I need the program running constantly. Media Center Master checks a couple different sites and then downloads the trailer. Sites like trailers.apple.com, youtube, imdb, and a few others, I think.
[It appears that reluctantflux desires the option of playing a single video from the "trailers" subfolder of that video.]
Are you able to add the option to first execute an external command whenever a video is played... and to wait until that external command is fully executed before beginning to play the video? If this was in place, I think I have everything else needed to play a random movie trailer prior to playing a movie. Currently if I do CTRL+2 from anywhere in WMC, it'll play a random movie trailer.
It would be preferable if this option could be enabled per Header Choice On Top option so it can be enabled for some but not for others. And it would be preferable if a different external command can be configured for each Header Choice On Top. For instance, this would allow me to play kids movie trailers for kids movies (which I have as a Favorite) and non-kids movie trailers for regular movies.
Being able to execute an external command could allow users to play pre-movie videos to enhance the theater ambiance, or execute an automation app to dim the lights, or any number of other things. If multiple things need to occur, the user could call a batch file.