Pulseaudio must be running (root is not needed):
systemctl --user start pulseaudio
Create fake microphone device zoom_input
:
pactl load-module module-null-sink sink_name=zoom_input sink_properties=device.description=zoom_input
pactl load-module module-remap-source master=zoom_input.monitor source_name=zoom_mic source_properties=device.description="zoom_mic"
Select it in system settings as default microphone
Play music:
mplayer -ao pulse::zoom_input East17-Steam.mp3