DC used to lump the graphics and sound into single compressed files and extract the file needed during the game. It became very slow for the editor to manage these files so I took it out. Just saving a design started taking 20-30 seconds to complete. I was using the free zip compression lib called ZLIB. That was long ago before DC came online.
I think I could add start/stop time for each music file in the background music queue. I already check the time for background music to transition day/night music. I'm not sure about the sound effects, but I suppose they could be put in the background queue with a specific start time.
I just looked at the help file for the BASS sound lib and I don't see that it supports fade in/out directly. I guess I would need to manipulate the volume myself. I'll add it to the list and see what I can come up with.
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CocoaSpud
Dungeon Craft Development Team
http://uaf.sourceforge.net