Thank you for the reference to gnmidi. This program looks like it might work for me.

Yes, it can be more of an art to hear the chords, so I fully suspect the program will be wrong sometime. But it will be a good place to start. A good program would look at the bass and chords (rhythem guitar, piano chords, etc) in a multitrack file, and ignore things like the melody, or maybe let the user select which tracks in a multitrack file to look at.

Thanks again for the references.