mpc-fade

#!/usr/bin/env bash
#
# mpd fade in / out script:
# 
#   fades the current mpc volume to the given <end volume>
#   within the given <duration in secs>
#
# Required tools:
#
#   sudo apt -y install mpc bc
#
# Typical usage in shell scripts or cronjobs:
#
# my /usr/local/bin/mpc-wakeme-up.sh looks like follows:
#
#!/usr/bin/env bash
#
# # play some playlist for 5 min, with 30 sec fadein and 5 sec fadeout
#
# mpc stop
# mpc clear
# mpc volume 15   # start with volume 15%
# mpc load "Radio Fantasy" # load a playlist
# mpc play
# mpc-fade 60 30  # fade to volume 60% within 30 sec
# sleep $((60*5)) # play for 5 min
# mpc-fade 0 5    # fade to volume  0% within  5 sec
# mpc stop
#
# EOF /usr/local/bin/mpc-wakeme-up.sh

readonly PROGRAM_FILE="$0"
readonly PROGRAM_NAME="$(basename $0)"

#echo >&2 "$PROGRAM_NAME: started from '$PROGRAM_FILE' with options: $*"

if [ $(( ${BASH_VERSINFO[0]} )) -lt 4 ]
then
  echo >&2
  echo >&2 "$PROGRAM_NAME: ERROR"
  echo >&2 "BASH version 4 or later is required."
  echo >&2 "You are running version: ${BASH_VERSION}"
  echo >&2 "Please upgrade."
  echo >&2
  exit 1
fi

require_cmd() {
  which "$1" >/dev/null
  if [ $? -ne 0 ]
  then
    echo >&2 "$PROGRAM_NAME: ERROR: Command '$1' is not found in the system path."
    return 1
  fi
  return 0
}

require_cmd sleep || exit 1
require_cmd bc    || exit 1
require_cmd mpc   || exit 1

MPC=`which mpc`
BC="`which bc` -l"

if [ $# -ne 2 ] ; then
   echo "usage: mpc-fade <end volume> <duration in secs>" ;
   exit 1 ;
fi

VOL=`$MPC volume | sed -e 's/[^0-9]*\([0-9]*\).*/\1/'`;

if [[ $VOL -eq $1 ]]; then
  echo "Volume $VOL already reached. Exiting." ;
  exit 0 ;
fi

D=`echo "$2/($VOL-$1)" | $BC`
D=${D#-}  # sleep duration absolute value

if [[ $VOL -lt $1 ]] ; then
  while [[ $VOL -le $1 ]] ; do
    $MPC volume $VOL > /dev/null ;
    VOL=$(($VOL + 1)) ;
    sleep $D;
  done ;
elif [[ $VOL -gt $1 ]] ; then
  while [[ $VOL -ge $1 ]] ; do
    $MPC volume $VOL > /dev/null ;
    VOL=$(($VOL - 1)) ;
    sleep $D;
  done ;
fi

exit 0