autonoteoff.py

"""
AutoNoteOff creates a virtual midi device with one midi input and one midi output
that passes through all events and outputs an additional note off immediately after every note on.

Usage:

python3 autonoteoff.py
(uses alsa midi, requires python3-pyalsa)

or 

python3 autonoteoff.py --jack
(uses jack midi, require python3-jack-client)
"""

from sys import argv
from time import sleep
from signal import signal, SIGINT, SIGTERM

running = True
def stop():
    global running
    running = False
signal(SIGINT, lambda a,b: stop())
signal(SIGTERM, lambda a,b: stop())

print('Press Ctrl+C to quit...')

name = 'AutoNoteOff'

if '--jack' in argv:
    import jack
    import struct
    client = jack.Client(name)
    inport = client.midi_inports.register('input')
    outport = client.midi_outports.register('output')
    NOTEON = 0x9

    @client.set_process_callback
    def process(frames):
        outport.clear_buffer()
        for offset, indata in inport.incoming_midi_events():
            # pass through
            outport.write_midi_event(offset, indata)
            if len(indata) == 3:
                status, note, vel = struct.unpack('3B', indata)
                if status >> 4 is NOTEON:
                    # output note off for every note on
                    outport.write_midi_event(offset, (status & 0b11101111, note, 0))

    client.activate()
    while running:
        sleep(0.01)
    client.deactivate()

else:
    from pyalsa import alsaseq
    server = alsaseq.Sequencer(clientname=name)
    port_type = alsaseq.SEQ_PORT_TYPE_MIDI_GENERIC | alsaseq.SEQ_PORT_TYPE_APPLICATION
    port_caps = (alsaseq.SEQ_PORT_CAP_WRITE | alsaseq.SEQ_PORT_CAP_SUBS_WRITE |
                 alsaseq.SEQ_PORT_CAP_READ | alsaseq.SEQ_PORT_CAP_SUBS_READ)
    port_id = server.create_simple_port(name, port_type, port_caps)

    while running:

        for event in server.receive_events():

            # pass through
            copy = alsaseq.SeqEvent(event.type)
            copy.set_data(event.get_data())
            copy.source = (server.client_id, port_id)
            server.output_event(copy)

            if event.type is alsaseq.SEQ_EVENT_NOTEON:

                # output note off for every note on
                data = event.get_data()
                noteoff = alsaseq.SeqEvent(alsaseq.SEQ_EVENT_NOTEOFF)
                noteoff.set_data({'note.channel': data['note.channel'], 'note.note': data['note.note']})
                noteoff.source = event.source
                server.output_event(noteoff)

        server.drain_output()
        server.sync_output_queue()
        sleep(0.01)