Add downbeats to midi using PrettyMIDI for use in Logic X

add_downbeats_from_syncpoints.py

import pretty_midi as pm
import json


def get_syncpoint_downbeat_times(syncpoints):
    downbeat_times = []
    for syncpoint in syncpoints:
        if len(syncpoint) == 2 or syncpoint[2] == 0:
            downbeat_times.append(syncpoint[1])
    return downbeat_times


def main(midi_file_path, syncpoints_file_path):
    syncpoints = json.load(open(syncpoints_file_path))
    downbeat_times = get_syncpoint_downbeat_times(syncpoints)

    midi_data = pm.PrettyMIDI(midi_file_path)

    # resolution - 1024 for music21, 220 for Logic Pro X

    output_midi = pm.PrettyMIDI(initial_tempo=120, resolution=1024)
    guitar = pm.Instrument(program=25)
    output_midi.instruments.append(guitar)

    output_midi.time_signature_changes.append(pm.TimeSignature(4, 4, 0))

    first_db = syncpoints[0][1]

    if first_db != 0:
        # this would be the proper way to do it, but it blows up the tick resolution
        # and the MIDI file won't save
        # output_midi._tick_scales.append((0, (60/(first_db / 4))*output_midi.resolution))
        # output_midi._update_tick_to_time(int(pm.MAX_TICK))

        # so instead we just force the first downbeat to be at 0
        downbeat_times[0] = 0

    for (db, n_db) in zip(downbeat_times, downbeat_times[1:]):
        if not n_db:
            n_db = midi_data.get_end_time()

        new_tempo = 60.0 / ((n_db - db) / 4)
        output_midi._tick_scales.append(
            (output_midi.time_to_tick(db),
             60 / (new_tempo * output_midi.resolution)))
        output_midi._update_tick_to_time(int(pm.MAX_TICK))
        # output_midi.time_signature_changes.append(pm.TimeSignature(4, 4, db))

    for instrument in midi_data.instruments:
        for note in instrument.notes:
            guitar.notes.append(note)

    output_midi.write('mona-lisa-output.mid')

    print("foo")


if __name__ == '__main__':
    midi_file_path = 'mona-lisa-transcribed.mid'
    syncpoints_file_path = 'mona-lisa-syncpoints.json'
    main(midi_file_path, syncpoints_file_path)