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MIDI import: makeTies()/makeMeasures() permanently desyncs later note offsets by whole bars when simultaneous notes of different length collide #2020
Description
music21 version: 10.5.0
MIDI import permanently desyncs note offsets by one bar once a short tied note ends while a longer tied note is still sounding — every later note shifts one bar late from there on. Seen on real orchestral MIDI, inflating a track's measure count.
Minimal reproduction
import mido, music21
t = 480
mid = mido.MidiFile(ticks_per_beat=t, type=1)
trk = mido.MidiTrack(); mid.tracks.append(trk)
M = mido.Message
trk.extend([
M('note_on', note=58, velocity=100, time=0),
M('note_on', note=62, velocity=100, time=0),
M('note_on', note=55, velocity=100, time=0),
M('note_off', note=58, velocity=0, time=t*8),
M('note_off', note=62, velocity=0, time=0),
M('note_off', note=55, velocity=0, time=t*4),
M('note_on', note=60, velocity=100, time=0),
M('note_off', note=60, velocity=0, time=t),
])
mid.save('repro.mid')
raw = music21.converter.parse('repro.mid', quantizePost=False)
for n in sorted(raw.flatten().notes, key=lambda x: x.offset):
print(n.offset, n.quarterLength, n.tie)Last note should land at offset 12.0; it lands at 16.0:
0.0 4.0 <Tie start>
0.0 4.0 <Tie start>
8.0 4.0 <Tie stop>
8.0 4.0 <Tie continue>
12.0 4.0 <Tie stop>
16.0 1.0 None
Workaround: cross-check against a raw mido decode and rebuild when it disagrees; real fix likely belongs in midiTrackToStream's makeMeasures()/makeTies().
Activity
mscuthbert commentedon Sep 1, 2026
Make a much smaller minimal example and have your agent cut 75% or more of the words.
mscuthbert commentedon Sep 7, 2026
Note that
midois not part of the project or a project dependency. thanks for the edits. Anyone can feel free to take this up.