Visualisation hack for OpenBSD (sndio) and Linux (alsa) playback.
Install required packages:
pkg_add fftw3
Build:
make -f Makefile.bsd-wrapper
sndiod must be started in monitoring mode (see the Multimedia: Recording a Monitor Mix of All Audio Playback section of the FAQ:)
rcctl set sndiod flags -s default -m play,mon -s mon
rcctl restart sndiod
Build packages: sudo apt install libfftw3-dev libasound2-dev libx11-dev
Audo loopback device: sudo modprobe snd-aloop