mediactrl: controlling laptop media buttons

My laptop media buttons don't do quite what I want. Specifically, I want

• Volume changes to affect multiple channels.
• A sound to play when I change volume.
• Play/pause, forward, rewind, and stop to control whatever application I'm using, not just always the same one (e.g., pause the video if I'm watching a video, but the music if I'm listening to music).

So I first wrote a script for volume changing and media control, then told KDE to call it when I press media buttons.

Modifying multiple channels and playing a sound on volume changes is trivial. Controlling multiple media players is trickier. A heuristic that works well is to have a list of players that are controlled in order. In my case, I first list my video players, kaffeine and kplayer, then my music player, amarok. Thus, since amarok is always running, the media buttons control it by default. However, when I watch a video with kplayer, the media buttons control it instead because I listed it before amarok.

The player list, and other parameters, are in a config file:

/etc/mediactrl.conf

################################################################################
# Volume settings
################################################################################

# What percent to step on volume up/down
VOL_STEP_PERCENT=5

# The sound to play when volume is changed
VOL_NOTIFICATION_SOUND="/usr/share/sounds/KDE_Click.wav"

# The player to use when volume is changed (default is /usr/bin/aplay)
#VOL_NOTIFICATION_PLAYER="/usr/bin/artsplay"

# Comma-separated list of channels to alter (default is "PCM")
VOL_CHANNELS="Master, Master Mono, Headphone, PCM"


################################################################################
# Media player settings
################################################################################

# Comma-separated list of media players in the order in which they should be
# checked. (these need to be the actual command name). For each of these, the
# command to be run when play/pause, stop, prev, and next are pressed should be
# specified. Examples are below.
MEDIA_PLAYERS="kaffeine, kplayer, amarok"

kaffeine_playpause='dcop kaffeine KaffeineIface pause'
kaffeine_stop="dcop kaffeine KaffeineIface stop"
kaffeine_prev="dcop kaffeine KaffeineIface posMinus"
kaffeine_next="dcop kaffeine KaffeineIface posPlus"

kplayer_playpause="dcop kplayer kplayer-mainwindow#1 activateAction player_pause"
kplayer_stop="dcop kplayer kplayer-mainwindow#1 activateAction player_stop"
kplayer_prev="dcop kplayer kplayer-mainwindow#1 activateAction player_backward"
kplayer_next="dcop kplayer kplayer-mainwindow#1 activateAction player_forward"

amarok_playpause="dcop amarok player playPause"
amarok_stop="dcop amarok player stop"
amarok_prev="dcop amarok player prev"
amarok_next="dcop amarok player next"

For each player, the config specifies commands to execute for each media button. Since I happen to use all KDE apps, these commands are calls to dcop. The config should be placed in /etc/mediacntrl.conf.

The script itself is below:

mediactrl

#!/bin/bash

function usage() {
  echo "Usage: mediactrl "
  echo "  playpause    - toggles play/pause on active media player"
  echo "  stop         - stops play on active media player"
  echo "  prev         - goes to previous on active media player"
  echo "  next         - goes to next on active media player"
  echo "  volume  - alters volume.  is up, down, mute, unmute, or toggle"
  exit
}

if [ ! -f /etc/mediactrl.conf -o ! -r /etc/mediactrl.conf ]; then
   echo "Cannot read /etc/mediactrl.conf!" >&2
   exit 1
fi
. /etc/mediactrl.conf

case "$1" in
   playpause|stop|prev|next)
       echo $MEDIA_PLAYERS | perl -ne 's/,\s*/\n/g; print' | while read PLAYER; do
           if pgrep -u "$USER" "$PLAYER" > /dev/null; then
               eval CMD="\${${PLAYER}_${1}}"
               [ -n "$CMD" ] && eval "$CMD"
               break
           fi
       done
       ;;
   volume)
       case "$2" in
           up|down)
               echo ${VOL_CHANNELS:=PCM} | perl -ne 's/,/\n/g; print' | while read CHANNEL; do
                   if [ -z "$VOL" ]; then
                       VOL=$(amixer get "$CHANNEL" | grep % | head -n 1 | sed -e 's/.*\[\(.*\)%\].*/\1/')
                       PLUS_MINUS=$(if [ "$2" = "up" ]; then echo "+"; else echo "-"; fi)
                       VOL=$((VOL $PLUS_MINUS ${VOL_STEP_PERCENT:=5}))
                       [ $VOL -lt 0 ] && VOL=0
                       amixer set "$CHANNEL" "$VOL%" > /dev/null
                       dcop kded kmilod displayProgress "Volume " "$VOL"
                   else
                       amixer set "$CHANNEL" "$VOL%" > /dev/null
                   fi
               done
               ;;
           mute|unmute|toggle)
               echo ${VOL_CHANNELS:=PCM} | perl -ne 's/,/\n/g; print' | while read CHANNEL; do
                   amixer set "$CHANNEL" "$2" > /dev/null
               done

               CHANNEL=$(echo $VOL_CHANNELS | sed -e 's/,.*$//')
               MUTE=$(amixer get "$CHANNEL" | grep % | head -n 1 | sed -e 's/.*\[\(.*\)\]/\1/')
               dcop kded kmilod displayText "Sound $MUTE"
               ;;
           *) usage;;
       esac

       [ -n "$VOL_NOTIFICATION_SOUND" ] && eval "${VOL_NOTIFICATION_PLAYER:=/usr/bin/aplay}" "$VOL_NOTIFICATION_SOUND" 1>/dev/null 2>&1
       ;;
   *) usage ;;
esac

The bit of craziness with setting volumes ensures all channels are truly set to the same level.

Note that this script was written for a laptop running Kubuntu, and may need tweaking for other settings. For example, it uses kmilo to display a volume bar, which will not work unless the kmilo service is running.

Once this script is executable (chmod u+x mediactrl), I map it to the laptop media buttons through the KDE Accessibility settings (K Menu -> System Settings -> Accessibility -> Input Actions). Voila! More intelligent media buttons.