Wdbinfo extracts information from a workman database file. This is what many audio-CD-playing programs, not just workman, use to store information about audio CDs. It's only really used for storing names of tracks etc., but can also be used for determining the length of a CD and each track on it, so it's possible for wdbinfo to give a complete list of what's on each CD without needing it to be in the CD-ROM drive.