OBS capture very laggy when not active window

[MajorDad]

Hello all!

First, I've searched a lot for this problem and found several tips and applied several of them, it's getting better but I still don't quite get why I'm getting such a difference.

Now let me explain. I run Microsoft Flight Simulator in VR with a Pimax Crystal on OpenXR. I'm using the OpenXR Mirror for OBS layer and it's perfect. Inside the VR session itself, I'm always getting very good results and FPS is smooth and pretty stable.

Now, independently of OBS currently streaming or recording, and no matter the settings I use, I always experience this: when OBS has focus (is the active window), capture seems very fluid, very similar to what I get in the VR session. When MSFS has focus (OBS is NOT the active window), the capture becomes laggy and choppy. Again, inside the VR session, it has no impact.

I've recorded the resulting experience. You'll see, it starts by OBS being in focus, then MSFS, then back again to OBS and the last bit in MSFS. It's very clear which is which.

Twitch

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www.twitch.tv

Any possible explanation or tips that could help me solve this?

Windows 11
RTX 4090
I7 10700 32 GB RAM
Game Mode is OFF.
HAGS is OFF.

Using Processor Lasso:
MSFS has it's own CPU set and priority set to HIGH
Pimax processes are own their own CPU set and priority set to HIGH
OBS is on a different CPU set and priority set to HIGH

 

[MajorDad]

Forgot my log file.

 

[MajorDad]

I do see a lot of this message:
[win_openxr_mirror] [OpenXR Mirror Capture] win_openxrmirror_init: Could not open file mapping object: 2

 

[MajorDad]

Ok so I seem to have discovered the source of the problem, but not the "why" it does that. I have another window capture in my OBS scenes that shows the content of a specific program displaying several stats. Well, when I disable that specific source, everything runs smoothly everywhere, independently of which window has focus.

As soon as I enable the source again and it shows up in the capture, I get the prior results of choppiness in OBS when it's not the active window.

Here's my recording of this.

Twitch

Twitch is the world's leading video platform and community for gamers.

www.twitch.tv

You can see in the top right corner when the other app is visible or not, and the effect on smoothness of the stream.

The question remains, why does it do that? It's a very simple app that shows some numbers, that's all.