download the package corresponding with your OS version, for instance x86/x64 /Linux/windows, from:
https://github.com/iteufel/nwjs-ffmpeg-prebuilt/releases
Extract the contents of the file in ~/Downloads/
As a result you will have a file called libffmpeg.so extacted in Downloads.
So, open a Terminal and go to the opera folder
cd /usr/lib/x86_64-linux-gnu/opera
then rename the original libffmpeg.so opera codec file:
sudo mv /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so.orig
Then copy the libffmpeg.so to /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so
sudo mv ~/Downloads/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so
Restart opera. Voilà
You can check in this link https://html5test.com that you are now H.264 capable :)
