Sgunhouse, you might want to take a look at Slackbuild for Opera ffmpeg codecs. There is no 'native' package for Slackware. Slackbuild, in this case, provides a script which downloads package for other distro (maybe Debian) and repackages it for Slackware. I am sure that you could modify the script to build a package for Mageia. Slackbuild can be found if you visit Slackbuilds.org, make sure to pick latest version and type 'opera' in the search input field.
Opera itself is provided as another Slackbuild, but don't let it bother you, there are no compatibility issues for codecs. I have, for example, downloaded RPM package directly from the site, converted it with rpm2tgz and installed as Slackware package. After that I downloaded and run Slackbuild for codecs. Everything worked without problem.
Thanks for the tab/window tip.