Everyone having problems with videos on Twitter (or GIFS) or with the H.264 codec videos. I'm running Opera 52 for Linux (Deepin 15, Ubuntu based).
I downloaded the last libffmpeg version from this github repo: https://github.com/iteufel/nwjs-ffmpeg-prebuilt/releases/tag/0.28.2
Just placed in the /usr/lib/x86_64-linux-gnu/opera and restarted Opera. All working like a charm! I've been searching for solutions like last 2,3 hours and finally found that solution. Hopes that helps some other Linux buddies here!