Running this script will start a tempo and broadcast it to the Arturia KeyStep 37, then wait for you to enter "s" to stop the clock. Example: `python midi-tempo-broadcast.py 125` to set BPM to 125.

midi-tempo-broadcast.py

# MIDI Tempo Broadcast
# Ross A. Reyman • soundcloud.com/r89music
# This script broadcasts a MIDI clock signal to hardware devices.
#
# prerequisites:
# - Python 3+
# - install Mido `pip install mido`
#
# Run this script with:
# `python midi-tempo-broadcast.py` OR
# `python midi-tempo-broadcast.py <bpm>`
# where <bpm> is the tempo in beats per minute.
#
# The default tempo is 125 BPM.

import mido
import time
import threading
import argparse
import sys

# Define constants: the name of the MIDI device and the initial tempo
DEVICE_NAME = 'Arturia KeyStep 37'
INITIAL_TEMPO = 125

# Check if the device is available
if DEVICE_NAME not in mido.get_output_names():
    print(f"\033[91mThe device '{DEVICE_NAME}' is not available. Check your MIDI connections.\033[0m")
    sys.exit(1)

def start_midi_clock(bpm, stop_event, current_bpm):
    # Calculate the delay between clock messages for the given tempo
    delay = 60.0 / bpm / 24

    # Open the output port
    with mido.open_output(DEVICE_NAME) as outport:
        # Send MIDI clock messages continually
        while not stop_event.is_set():
            start_time = time.perf_counter()

            # Check if the tempo has changed
            if bpm != current_bpm[0]:
                bpm = current_bpm[0]
                delay = 60.0 / bpm / 24

            # Send a MIDI clock message
            msg = mido.Message('clock')
            outport.send(msg)

            # Calculate the actual delay taking into account the time spent sending the message
            actual_delay = delay - (time.perf_counter() - start_time)
            actual_delay = max(0, actual_delay)  # Ensure the delay is not negative

            # Sleep for the calculated delay using time.perf_counter
            while time.perf_counter() - start_time < actual_delay:
                pass

def wait_for_stop_command(stop_event, current_bpm):
    # Wait for user input in a loop
    while True:
        command = input("\033[2mEnter 's' to stop the MIDI clock or a number to change the tempo: ")
        if command.lower() == 's':
            stop_event.set()
            break
        elif command.isdigit():
            current_bpm[0] = int(command)
            print(f"\033[2mThe current tempo is now: \033[92m{current_bpm[0]} BPM.\033[0m")

# Create a stop event
stop_event = threading.Event()

# Parse command-line arguments
parser = argparse.ArgumentParser(description='Start a MIDI clock with a specified tempo.')
parser.add_argument('bpm', type=int, nargs='?', default=INITIAL_TEMPO, help='The tempo in beats per minute.')
args = parser.parse_args()

# Print the initial tempo
print(f"\033####################################################")
print(f"\033[2mThe initial tempo is: \033[92m{args.bpm} BPM.\033[0m")

# Create a shared variable for the current BPM
current_bpm = [args.bpm]  # Default BPM

# Start the MIDI clock at the specified BPM in a new thread
clock_thread = threading.Thread(target=start_midi_clock, args=(args.bpm, stop_event, current_bpm))
clock_thread.start()

# Start the command listener in a new thread
command_thread = threading.Thread(target=wait_for_stop_command, args=(stop_event, current_bpm))
command_thread.start()