I needed to install mpv, which failed with this error:

:~$ mpv '/my/file.mp4'
mpv was compiled and linked against a mixture of Libav and FFmpeg
versions. This won't work and will most likely crash at some point.
Exiting.

This took me quite some time to debug. The reason appears to be
incompatibility with the version and dependencies from "deb
http://packages.devuan.org/merged" (which I use exclusively, except
for special purposes).

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=753090
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785650

I noticed that quite a few packages originating from deb-multimedia
are on my system, installed from "/merged".

My quick fix was install mpv direct from deb-multimedia (but yet
another 3rd-party repo to configure)

Packages from deb-multimedia have also been reported and seen here to
break vlc also at various times in the past.

What is, or will be, official Devuan policy on this?