Now hear this, Solarian polyglots.
Open Terminal.
~ $ anki
mpv too old, reverting to mplayer
But, of course, mplayer isn't in our repo. But our mpv looks up-to-date. Our Anki, however, does not. It's 2.1.16-13. The latest Anki is 2.1.20. Little history: Anki always has audio dependency versioning issues with mpv and mplayer across the distroverse. They just can't seem to sync their projects or bundle their own player.
Current solution? The official method of distribution on the Anki website is incredibly easy. You just run it as a portable app or install via make system-wide. It's all in the readme. And it works with Solus' mpv version as of 02-17-2020.
Should our Anki package be updated? Sure. But it will probably unnecessarily break again the next time mpv updates.