I found a nice feature in the preferences of my instant messenger gajim, where a check box says "Set status message to reflect currently playing music track". My only problem was that i could not enable the option, because it was greyed out and not active. First I tried to find a plugin for my musicplayer rhythmbox, but the information I found seemed to be old and several web pages said that gajim and rhythmbox should work together natively. I remembered that most GNOME applications use D-Bus to communicate with each other. I supposed that there was a D-Bus package missing on my Sidux system, so I searched the package repository with "apt-cache search dbus" and found a package named "python-dbus". Since I know that gajim is written in python I installed the package and had success: After a restart of gajim the option was now available and worked when enabled.
Solution worked with gajim 0.11.4 and rhythmbox 0.10.1.