I had a problem with the thumbnails not being generated for an H.265 video. After removing totem.thumbnailer from /usr/share/thumbnailers, sure enough, the thumbnail was generated just fine. I thought to try and use Totem to play the video, and I get this:
The thing is that I do have the decoder installed, and I can play this same video just fine in MPV.
I then found a bug report that seems to be about the same issue, but the ticket got bounced around and then forgotten about. Reading that ticket, I don’t really understand where exactly the problem lies and where I should open a new ticket. Is this a problem with Totem itself? GNOME Software? Packagekit? RPM Fusion? What is the right place for this?
Totem uses Gstreamer for video codecs, mpv doesn’t. So it is normal for mpv to play a video while Totem can’t play the same video. Do you have gstreamer1-plugins-bad-free package installed?