Adjust audio volume level with CLI omxplayer - Raspberry Pi

to provide more precise information for playing through scripts, there are 3 ways to change sound volume in current version of omxplayer, and values are not so intuitive:

1. on starting command line, param --vol YYY, double millibels, default 0, range [-6000:0]
2. by stdin interface, sending +/- to omxplayer will increase/decrease volume for 300 dmbels
3. with DBUS interface, cmd 'set volume', value double:XXX, default 1, range [0:1]

xxx to yyy relation is: XXX = 10 ^ (YYY / 2000) ... according to omxplayer.cpp source code, reverse formula would be: YYY = 2000 * (log XXX).

so if we need:

• volume 1%, XXX=0.01 and YYY=-4000 (10^(-4000/2000)=10^-2=0.01
• volume 10%, XXX=0.1 and YYY=-2000 (10^(-2000/2000)=10^-1=0.1
• volume 50%, XXX=0.5 and YYY=-602 (10^(-602/2000))~=0.5
• volume 100%, XXX=1 and YYY=0 (10^(0/2000)=10^0=1)
• volume 150%, XXX=1.5 and YYY=352 ... (for boost test, normal values are <=100%)

working bash script for dbus volume command:

export DBUS_SESSION_BUS_ADDRESS=$(cat /tmp/omxplayerdbus.${USER:-root})dbus-send --print-reply --session --reply-timeout=500 \           --dest=org.mpris.MediaPlayer2.omxplayer \           /org/mpris/MediaPlayer2 org.freedesktop.DBus.Properties.Set \           string:"org.mpris.MediaPlayer2.Player" \           string:"Volume" double:0.5   # <-- XXX=0.5 (50% sound volume)

equals to volume parameter at startup:

omxplayer --vol -602 mediaFileName.mp4

... both sets sound volume to 50%.

I am not sure how to adjust the volume level with a command. But when using the omxplayer CLI, just press - or + to turn the volume up or down.

Omxplayer doesn't use alsa for sound output, but it's possible to use stdin interface

Volume up:

echo -n "+" > /proc/$(pidof omxplayer.bin)/fd/0

Volume down:

echo -n "-" > /proc/$(pidof omxplayer.bin)/fd/0