I upgraded to Fedora 26 weeks ago but I realize only today that I was having issues playing videos in Firefox, while I was trying to attend an online course.
At first I thought it was Flash Player’s fault: I always forget to have it and I always forget to update it. It was indeed out-of-date but the annoying “The media could not be played” error message was still there.
After a quick research and a little help from HTML5test, I noticed that few codecs were missing. I prefer not to install a bunch of codecs that I don’t even know what they’re for; if I am missing something I’m pretty sure it’ll come out!
It’s perfectly OK that Fedora doesn’t provide the codecs you might need (remember, Free as in freedom), so if you need them you can just download the .rpm or configure RPM Fusion Repositories:
dnf install https://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-$(rpm -E %fedora).noarch.rpm https://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-$(rpm -E %fedora).noarch.rpm
This will install free and nonfree repos.
In my case, I had to install these:
x264-0.148-20.20170519gitd32d7bf.fc26.x86_64 : H264/AVC video streams encoder Repo : rpmfusion-free ffmpeg-3.3.3-4.fc26.x86_64 : Digital VCR and streaming server Repo : rpmfusion-free-updates
Restart you browser and you’re done.