you'd have to use a video capture unit such as used by game streamers etc.
But what are you trying to achieve?
Unless there's some of sort of repeating error there's not going to be anything displayed the console. It will simply sit at the login prompt with the MOTD telling you where access the webgui.
There won't be any output from any of the VMs or LXCs
Otherwise you might as well have a SSH shell open.
some of sort of repeating error
That's exactly why I want to do this. I've had some issues and want to be able to check for errors at will from any PC on the LAN and also when not at home.
You could do something like an LK373 transmitter (preferably a v3) - it's normally part of an "HDMI over Ethernet extender" transmitter/receiver pair, but all it really does is capture HDMI and output it to the network as an RTSP stream that you can view with ffmpeg or VLC (no need for the Receiver). They're about $45 on AliExpress.
(I use one to capture the output of a cable box at home, then proxy it through xTeVe to Plex as a live TV channel.)
Brilliant, i was looking for something like this as well for a project, thanks!
Correction: model is the LKV373A
Lots of info here: https://blog.danman.eu/new-version-of-lenkeng-hdmi-over-ip-extender-lkv373a/
There are several versions of it out there, make sure to get a v3 (v2 is older and not as full-featured, v4 is partially encrypted and not well-supported).
It can be a bit tricky to get it set up initially (especially since it uses an incomplete implementation of Multicast), but once it's going it can be quite solid. Feel free to PM me if you have questions and I'll do what I can to help.
If you just want video then HDMI capture card like the other replies.
If you wanted HDMI output and also input keyboard/mouse, another PC with a USB Crashcart device or PiKVM
HDMI output and also input keyboard/mouse
Preferably. I remember now reading about PiKVM some time back. I will look into it again.
If your Proxmox box has an Intel CPU with AMT, like the vPro series of CPUs, that's basically a built-in BMC without a dedicated network interface. Once you configure it with the like of MeshCentral, you can remotely manage the Proxmox box, including full display replication.