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#!/usr/bin/env python3
"""A simple JACK timebase master."""
import argparse
from threading import Event
import jack
class TimebaseMasterClient(jack.Client):
def __init__(self, name, *, bpm=120.0, beats_per_bar=4, beat_type=4,
ticks_per_beat=1920, conditional=False, debug=False, **kw):
super().__init__(name, **kw)
self.beats_per_bar = beats_per_bar
self.beat_type = beat_type
self.bpm = bpm
self.conditional = conditional
self.debug = debug
self.ticks_per_beat = ticks_per_beat
self.stop_event = Event()
self.set_shutdown_callback(self.shutdown_callback)
def shutdown_callback(self, status, reason):
print('JACK shutdown:', reason, status)
self.stop_event.set()
def timebase_callback(self, state, nframes, pos, new_pos):
if self.debug and new_pos:
print('New pos:', jack.position2dict(pos))
# Adapted from:
# https://github.com/jackaudio/jack2/blob/develop/example-clients/transport.c#L66
if new_pos:
pos.beats_per_bar = self.beats_per_bar
pos.beats_per_minute = self.bpm
pos.beat_type = self.beat_type
pos.ticks_per_beat = self.ticks_per_beat
pos.valid = jack.POSITION_BBT
minutes = pos.frame / (pos.frame_rate * 60.0)
abs_tick = minutes * self.bpm * self.ticks_per_beat
abs_beat = abs_tick / self.ticks_per_beat
pos.bar = int(abs_beat / self.beats_per_bar)
pos.beat = int(abs_beat - (pos.bar * self.beats_per_bar) + 1)
pos.tick = int(abs_tick - (abs_beat * self.ticks_per_beat))
pos.bar_start_tick = (
pos.bar * self.beats_per_bar * self.ticks_per_beat)
pos.bar += 1 # adjust start to bar 1
else:
assert pos.valid & jack.POSITION_BBT
# Compute BBT info based on previous period.
pos.tick += int(nframes * pos.ticks_per_beat *
pos.beats_per_minute / (pos.frame_rate * 60))
while pos.tick >= pos.ticks_per_beat:
pos.tick -= int(pos.ticks_per_beat)
pos.beat += 1
if pos.beat > pos.beats_per_bar:
pos.beat = 1
pos.bar += 1
pos.bar_start_tick += pos.beats_per_bar * pos.ticks_per_beat
if self.debug:
print('Pos:', jack.position2dict(pos))
def become_timebase_master(self, conditional=None):
if conditional is None:
conditiona = self.conditional
return self.set_timebase_callback(self.timebase_callback, conditional)
def main(args=None):
ap = argparse.ArgumentParser(description=__doc__)
ap.add_argument(
'-d', '--debug',
action='store_true',
help='enable debug messages')
ap.add_argument(
'-c', '--conditional',
action='store_true',
help='exit if another timebase master is already active')
ap.add_argument(
'-n', '--client-name',
metavar='NAME',
default='timebase',
help='JACK client name (default: %(default)s)')
ap.add_argument(
'-m', '--meter',
default='4/4',
help='meter as <beats-per-bar>/<beat-type> (default: %(default)s)')
ap.add_argument(
'-t', '--ticks-per-beat',
type=int,
metavar='NUM',
default=1920,
help='ticks per beat (default: %(default)s)')
ap.add_argument(
'tempo',
nargs='?',
type=float,
default=120.0,
help='tempo in beats per minute (default: %(default)s)')
args = ap.parse_args(args)
try:
beats_per_bar, beat_type = map(float, args.meter.split('/'))
except ValueError:
ap.error('Invalid meter: ' + args.meter)
try:
tbmaster = TimebaseMasterClient(
args.client_name,
bpm=args.tempo,
beats_per_bar=beats_per_bar,
beat_type=beat_type,
ticks_per_beat=args.ticks_per_beat,
debug=args.debug)
except jack.JackError as exc:
ap.exit('Could not create timebase master JACK client: {}'.format(exc))
with tbmaster:
if tbmaster.become_timebase_master(args.conditional):
try:
print('Press Ctrl-C to quit...')
tbmaster.stop_event.wait()
except KeyboardInterrupt:
print('')
finally:
try:
tbmaster.release_timebase()
except jack.JackError:
# another JACK client might have grabbed timebase master
pass
else:
ap.exit('Timebase master already present. Exiting...')
if __name__ == '__main__':
main()
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