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 <version>-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.

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

Put libffmpeg.so in the lib_extra folder.