Automatic metronome track?

[Michael Ellis]

I want to automate the process of generating a midi metronome track
for rehearsal purposes.  It's trivial if the piece is in the same
meter throughout,  e.g. if the piece has 97 measures in 4/4 you can
do:

        \new Voice = "Click" {
            \set midiInstrument = #"woodblock"
            \repeat unfold 97 \drums {wbh4 wbl wbl wbl}
        }

but what if the meter is frequently changing? I'm transcribing the
baritone part out of a large new work that, no exaggeration, seldom
goes more than a few bars without changing meter.   I googled various
combinations "LilyPond", "metronome", "click", & "measure" but didn't
find anything.  Is there a scheme function I can use to detect the
start of a measure and the current meter?  Or some other way to
accomplish the same thing.  I want to end up with a music function
that looks like

     \clickTrack \mymusic

that will scan through a music variable, \mymusic,  and return a
"wbh" on each downbeat and a "wbl" on the remainder.


Cheers,
Mike