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pacmd
pavucontrol

$ pacmd list | grep "active port"
  active port: <hdmi-output-0>
  active port: <analog-output-lineout>
  active port: <analog-input-linein>
pacmd set-sink-port 0 analog-output-lineout

/etc/pulse/default.pa:
set-sink-port 0 analog-output-lineout