@parduspars I think it's a problem in Linux due to patents/licences, the included libffmpeg (e.g. /usr/lib64/opera*/libffmpeg.so) doesn't work for me either.
Check out https://github.com/nwjs-ffmpeg-prebuilt/nwjs-ffmpeg-prebuilt/releases for precompiled versions with support for more codecs, which make videos from IG and X work.
Also see here:
https://github.com/nwjs-ffmpeg-prebuilt/nwjs-ffmpeg-prebuilt/blob/master/guides/build_linux.md#opera-browser-issue