speakerd

#!/bin/bash
# turns power supply for active speakers on/off when sound is played/not played
# very handy on a RaspberryPi with active speakers
# you need to install "gpio" from http://wiringpi.com/ first
# see http://wiringpi.com/pins/ for pin numbers
# run this as service with
#[Unit]
#After=mpd.target
#[Service]
#ExecStart=/speakerd
#Restart=always
#[Install]
#WantedBy=multi-user.target

PIN=5

function playing {
  grep RUNNING /proc/asound/card*/*p/sub*/status >/dev/null
}

function speaker {
  echo "speaker $1"
  gpio mode $PIN output
  [ "$1" = on ] && gpio write $PIN 0 || gpio write $PIN 1
}

STATE=unknown
PLAYING=0

speaker off

while true; do
  playing && PLAYING=3
  if [ $PLAYING -gt 0 ]; then
    [ $STATE != on ] && speaker on
    STATE=on
    ((PLAYING--))
    sleep 10
  else
    [ $STATE != off ] && speaker off
    STATE=off
    sleep 1
  fi
done