Installing backends

soundKonverter is a so called frontend providing an easy to use graphical user interface to convert audio files. It relies on so called backends, programs that can be started in the background to do the actual conversion. So in order to be able to convert files, you need the necessary backends installed. For a list of all supported backends and their respectively supported file formats, have a look at Supported plugins and formats.

Using the package manager

Some of the backends might be part of your linux distribution, some won't. And this differs between various distributions. So a good start is to check whether the backend you are trying to install is already provided by your distribution.
All linux distributions have a package manager. Start it and search for the backend you wish to install. Be sure to try different notations if you can't find it straightaway. If you can find it, then install it and you're done (don't forget to restart soundKonverter, though). Otherwise you will have to find a package somewhere else or install it manually.

Finding additional package repositories

Most linux distributions provide an additional package source where you can find multimedia packages that can't be provided by the distribution directly due to licensing issues. Some examples include:

openSUSE: Packman repository
Ubuntu: Repositories universe and multiverse

You should find out whether your distribution provides such a repository because you will find much more packages there useful beyond soundKonverter.

Ubuntu distribution contains following packages, all can be installed by following apt command:

apt install cdparanoia faac ffmpeg flac flake fluidsynth lame musepack-tools mplayer sox speex timidity twolame vorbisgain wavpack

For aacgain, libav, mac, mp3gain, musepack, neroaac, opustools, shorten, ttaenc or vorbistools you will most probably need to build them from their sources.