

Aha, ok, so it’s using pipewire when logged in locally, and it can’t find it when using it remotely.
Can you try logging in via ssh again and checking if there’s a /run/user/$UID/pipewire-0 (or other pipewire-<NUMBER> sockets)?
If there isn’t, that means your pipewire service isn’t running, you can try starting it with systemctl --user start pipewire wireplumber. You may need a loginctl enable-linger $USER and a re-login for that to work. You can also do systemctl --user enable pipewire wireplumber so that it auto-starts them whenever you log in, if that’s not already the case.
If/once that socket is there, you may need to export XDG_RUNTIME_DIR=/run/user/$uid so that mpv can find the socket. You should probably do that in your .profile so it’s set automatically.






I think that’s distinct from what the user is trying to do. They are trying to play audio and video on the machine that’s running the ssh server, by outputting video over HDMI from the graphics card and sound over the 3.5 mm jack. There’s no X forwarding to the ssh client going on.