If there is (more or less "KDE-native"), I'm pretty sure you can find it from kde-apps.org
Remember though, that every time you convert a compressed video or audio format to another one (mp3 to ogg, mpeg to avi, ...) you lose quality because decoding doesn't increase quality, but recompression loses each time. It might not be something you hear with cheap speakers, but often compressed formats are already so lossy and bad quality that losing more is not an option. If you just can, don't convert a compressed format to another one, instead get the original (hopefully uncompressed) media and recode it to the format you need. CD audio, for example, has more quality than an mp3 file created out of it, but the same track in ogg format (directly from the cd) has better quality than if you make the ogg out of the mp3 and not the cd directly.