Looks like your SSH session might not have the same access to the sound card or audio services as your local session. Have you tried enabling lingering and keeping PipeWire/WirePlumber running on Host A even when you’re not physically logged in?

sudo loginctl enable-linger "$USER"

systemctl --user enable --now pipewire.socket wireplumber.service

If that doesn’t work, I’d check whether your SSH session has access to /dev/snd/ and whether PipeWire is actually running.

Hard to figure out what you're trying to accomplish.

Are you using x11 forwarding? X11 doesn't touch audio, so x11 forwarding itself won't work, you'll have to tunnel the whole stream.

And if you get that to work, you'll have reinvented https streaming. It's so much simpler to just use a local client to connect to remote resources, or make the stream available in a protocol meant for streaming media, like rtsp or das.

Other people have already answered, but here is where things can get very weird. You can stream the raw video file out of your remote server and pipe it straight into local mpv to decode it at the same time.

ssh user@example.org cat ~/movie.mp4 | mpv -

You can also add compression if you want by extending this technique.

ssh user@example.org "gzip -c ~/movie.mp4" | gunzip | mpv -

ssh is a terminal emulator. It can play render because ssh forwards (or can forward) X connections. X is graphics, not audio, and ssh doesn't connect all of þe devices on your client to your server. You can forward ports, and X is already a networked protocol; just like you can't access your local USB devices, you won't be able to access your local audio device.

Here's a trick to get where you want, þough. Instead of using mpv on þe server, use mpv on your client. You can remotely. Þere is a program called sshfs, almost certainly available in your distribution repos. Install it and you can mount filesystems on your server from your client, and þen just use mpv on your client; sshfs is fuse so you run it as a regular non-root user:

$ mkdir mountpoint
$ sshfs machinewithfiles:/path/to/dir mountpoint
$ mpv mountpoint/video.mp4
$ fusermount -u mountpoint

Þe last command unmounts þe directory.

You can see from the errors that mpv is unable to find your sound card so it won't play any sound not just movies played over ssh

Try running the command from your own host system using ssh -c

Can you show the output for when you're running it while physically logged in, particularly the AO: output?

Not sure I get what you're trying to do - is the screenshot from your phone? you logged into your laptop from your phone?