I consider myself multimedia challenged and naive. With my new box, slowly I am learning about the field. Recently one person described Slackware as "DRM compliant" and I think that observation is a fair description. In other words, the stock Slackware will support playing common formats, but don't expect much else for other tasks, such as ripping or mastering your own disks. K3B will help as a front-end to such tasks, but without the underlying codecs and support libraries,
K3B is not going to help.
I hope to post at my web site a how-to sharing what I have learned to improve multimedia with the stock Slackware. I have built and added a few dozen packages that don't come with the stock Slackware. For now, consider browsing the
slackbuilds.org site for some insight into how much multimedia support is absent from the stock Slackware. As a starter, you might want to download, build, and install the
codecs package. The package is really little more than an installation wrapper containing all the codecs. I use xine most of the time for my video needs, but I also built the
mplayer package because so many other video/audio tools depend upon mplayer (mencoder) for support.
There also is the slacky.eu site. As much I am pleased with the sheer volume of additional build scripts there, I have found that quality control is sometimes lacking as I have struggled to get some scripts to build. I have not had that issue with slackbuilds.org.
Regardless, if you want Slackware to be a full fledged multimedia box, you'll have to roll up your sleeves and start building packages. I have learned much the past many weeks building all of this support.