When you want an easy solution. I'm building ffmpeg.so packages for archlinux for the different opera flavours. Since these are statically linked they should be usable on any linux distribution.
The packages can be found at http://repo.herecura.eu/
You can browse the packagelist where you should be able to find:
opera-ffmpeg-codecs-*
opera-beta-ffmpeg-codecs-*
opera-developer-ffmpeg-codecs-*
Most of the time the versions are the matching versions where the opera branch was based on. For developer the versions might divert a bit due to issues in the chromium source.