Is there a possibility to add this package to Opera's repository?

No. License restrictions.

So I need to contact ffmpeg developers? or the chromium project?

Ubuntu has in it's repositories a package called "chromium-codecs-ffmpeg-extra" that is needy to play some youtube/twitter videos (anyway not only these two services). There are linux distribuitions that there's no this package in it's repositories, like Debian! Is there a possibility to add this package to Opera's repository?