Adjust audio volume level with CLI omxplayer - Raspberry Pi

I have a bash script that plays .mp3 files on my Raspberry Pi via omxplayer. But can not control the local (earphone) audio volume with the GUI. Is there a command for the CLI that I can implement in the bash script? I have searched quite a bit, but can not find such a command.

Code:

omxplayer Song_Title.mp3

Set audio for local (earphone) output:

sudo modprobe snd_bcm2835 sudo amixer cset numid=3 1

omxplayer -o local

Thanks!

Solution

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:

on starting command line, param --vol YYY, double millibels, default 0, range [-6000:0]
by stdin interface, sending +/- to omxplayer will increase/decrease volume for 300 dmbels
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%.