Hi, I found the solution, it was missing the "chromium-codec-ffmpeg-extra" package
Posts made by barezb
RE: [Solved]HTML 5 video not working on Linux Mint 18 on OperaOpera for Linux
[Solved]HTML 5 video not working on Linux Mint 18 on OperaOpera for Linux
I can't play HTML5 videos on Opera. I have the latest version of Opera and i have already tried removing it and installing it again.
I was using Linux Mint 17.3 Cinnamon and it was working fine, but since my upgrade to Linux Mint 18 Cinnamon, HTML5 videos don't show. I once got a system update for gstream packages, and it started working again. Later on, I got another update for Kernel update 4.4.0-31, and HTML5 videos stopped working again on Opera. Then I installed all the gstream* packages thinking it would solve the problem, but it didn't.
HTML5 videos work fine on Firefox.