You cant layer ffmpeg, you need to override-remove everything libav and then install everything new from rpmfusion. I did that, its a mess.
If you just want video playback thats just libavcodec-freeworld, thats why I specifically mentioned ffmpeg.
I am not a fan of Distrobox for small tools. For sure possible but unnecessary and the workflow is a pain. And trust me, I use it daily and even ran libvirt in a rootful one, virt-manager in a rootless one, connected over ssh.