From Salix OS

The answer to this question varies, depending on the installation mode you used when installing Salix and what codecs you have installed yourself after installation through the package management. So it basically depends on what you already have installed in your system.

• If you have done a full mode installation, then you already have installed all codecs needed for playback of free formats. So, what salix-codecs-installer does in that case, is install patent encumbered codecs, along with their respective gstreamer plugins, so that you will be able to play mp3 audio files, mpeg4 videos and encrypted DVDs.
• If you have done a basic mode installation, then no multimedia codecs are installed by default. So, in that case, salix-codecs-installer installs all codecs, include free and patent encumbered ones, along with their respective gstreamer plugins.
• Anything in between (or not), will install everything that is missing so you can playback any kind of multimedia format. If you already have everything installed, salix-codecs-installer will just check that everything is installed.

In any case, you could achieve the same result, if you launched gslapt (or using slapt-get from the CLI) and selected to install any codecs you want and you can still do that if you want to have more control on your system.

If you're interested to know exactly which packages get installed by salix-codecs-installer (the "Install multimedia codecs" menu option) you can take a look in the package list in your system's /usr/share/salix-codecs-installer/pkglist (you need to have salix-codecs-installer to have that file). That will probably include packages that are already installed in your system, but salix-codecs-installer checks for their presence anyway, because they are direct dependencies of the codecs libraries listed in that same file.