Fedora Linux

Due to licensing issues, ffmpeg and its encoders/decoders were always a pain point to new users on Fedora (and it will still require some manual intervention to get everything working correctly due to those licensing issues), BUT it's halfway there now, because ffmpeg is finally coming to the main repos of the distro, with the codecs that they are able to provide without potential legal trouble.

See here a list of supported decoding and encoding codecs.

You'll notice a lack of H264 decoders there. That's the main pain point I was talking about. You'll still need RPMFusion to get it, but for most other cases you'll be able to get it directly from the repos.