What exactly does headless mode do?

[Wordsmith9091]

I haven't been clear on what happens with that checkbox selected.

If I have my physical displays connected, I'm not seeing it have any effect -- they stay on, and the normal primary remains the primary until the first time I reassign it in the Windows Display settings after connecting with a given client.

If my physical displays are all off when I connect, it still connects with the virtual display whether I've got "headless" checked or not.

What am I missing?

This is all on Win 11 24H2

[ClassicOldSong]

I remember I've already answered this question somewhere, but I can't remember where...

Headless mode skips the initial decoder probing and only do it when a stream is about to start. It'll force all connections to attach a virtual display(in true headless configurations, a virtual display is always needed).

Windows 11 24H2 broke the way to set primary display programatically, and primary display isn't related to headless mode.

[Wordsmith9091]

Thanks as always for the quick answers.

So if I have headless selected while physical displays are connected, using 24H2, it'll always stream the virtual display, but that may or may not become the primary display depending on whether I set it to be last time that client connected. And it won't (because it currently can't) shut off the physical displays.

If I have headless not selected and there are no physical displays connected, it'll still spin up a virtual display and use it, but it'll try to do the initial decoder probing.

Is that about right?

[ClassicOldSong]

If you want to shut off your display you need to change to "Show only on 2", but some monitors doesn't seem follow the config, so it might not be able to disable it on some monitors.

If headless mode isn't selected and there's no physical display connected, and you don't initiate virtual display from client, it'll fail to start, the initial probing will also fail.

[Wordsmith9091]

And/or if I have the option on a per-app basis to force the display, correct?

[ClassicOldSong]

Yes, just check Always use Virtual Display in the app you want.