h264-live-player VS nwjs-ffmpeg-prebuilt

You need libffmpeg. You can download a prebuilt one from here. Put libffmpeg.so file to lib_extra directory at Opera's installation directory (probably /usr/lib64/opera).

How to Install libffmpeg (for proprietary h.264 and aac support) for Opera for Linux_x64 Goto the URL opera://about and look at the "Browser identification" (User-Agent) string to see what major version of Chromium Opera is using (79, 80, 81, 82 etc.). Also, take note of the "install" path. You'll need that later. Goto https://github.com/iteufel/nwjs-ffmpeg-prebuilt/releases/ and download the latest -linux-x64.zip that's built with the same major version of Chromium that your Opera is. For example, if your Opera is built with Chromium 79, goto https://github.com/iteufel/nwjs-ffmpeg-prebuilt/releases/tag/0.43.6 and download 0.43.6-linux-x64.zip. Or, goto https://packages.ubuntu.com/search?keywords=chromium-codecs-ffmpeg-extra and click on the link to the distro that has "chromium-codecs-ffmpeg-extra" for the version of Chromium you need. Then, on the page for the distro, click the "amd64" link to goto the download page. On the download page, you can download the deb file and then extract it to get libffmpeg.so out of it. For example, if you need libffmpeg.so for Chromium 81, goto https://packages.ubuntu.com/focal-updates/amd64/chromium-codecs-ffmpeg-extra/download and download the the deb file. (in this case though, ignore that and use the libffmpeg.so in http://security.ubuntu.com/ubuntu/pool/universe/c/chromium-browser/chromium-codecs-ffmpeg-extra\_83.0.4103.61-0ubuntu0.18.04.1\_amd64.deb that's from https://packages.ubuntu.com/bionic/chromium-ffmpeg-extra even though it says it's for Chromium 83) If nothing works, try a libffmpeg.so for the next version of Chromium and so on. Once you have the zip/deb file, extract it to get libffmpeg.so. Then, create the folder lib_extra in Opera's install folder that you took note of in opera://about earlier and put libffmpeg.so in the lib_extra folder. The path to libffmpeg.so should then be opera_install_folder/lib_extra/libffmpeg.so. On Linux Mint, that'd be /usr/lib/x86_64-linux-gnu/opera/lib_extra/libffmpeg.so. On Arch Linux, it might be /usr/lib64/opera/lib_extra/libffmpeg.so. Again, goto the URL opera://about in Opera and look at the "install" path.