Unfortunately there is currently no playlist management within Mopidy (the underlying music server).
But if you put some m3u playlist files in your playlist directory (/var/lib/mopidy/playlists) they will appear in the web interface’s playlist section. There are some examples at http://en.wikipedia.org/wiki/M3U.
You can manually create the playlist files yourself (a bit of a pain for large playlists)
Try to use a program on another computer (a bit tricky since you’ll need to plug your USB stick into the other computer and then ensure the file paths of the items within the generated playlist are correct for musicbox).
Or I think there is the option of installing beets on your RaspberryPi and using that to create/manage your playlists. I don’t use it myself so but I know some people on here do (along with mopidy-beets or mopidy-beets-local).
I didn’t think it was really worth mentioning the partially working playlist management features that few (if any) web clients try to use. But Mopidy is constantly improving and playlist management is on the roadmap so stay tuned!
Yeah, it’s not something I’d recommend for end users right now, I was just nitpicking here
BTW, the current Mopidy-Mobile beta already does support saving the tracklist as a local playlist, but that’s not something I’d recommend for general use, either…
It has a link to a site where you can download a script that creates a playlist from a directory holding mp3 files.
In order for it to work properly you need to get the ffmpeg / ffprobe binaries for rpi.
I have created a wrapper script that calls the original script for each directory of a certain folder. In my case I call it for /music/MusicBox and it creates playlists for each subdirectory and puts them in /music.
I created a small python script to generate a playlist from tracks in your local mopidy database. More as an exercise in python programming (new to me). It works fine for my MusicBox setup so it might be of some use for other users.