Question / Help Adding a capture card source lags OBS

betawarz

betawarz

New Member
Hi folks,

I'm trying to optimize my two PC streaming setup. I recently purchased a very nice capture card - Magewell Capture 4K Plus. The card can easily handle high resolutions and also supports 144Hz input signal.

So, I've got my gaming PC's graphics card connected with the streaming PC's capture card via HDMI. I can use the software that comes with my capture card to preview the video stream. This works flawlessly and has no noticeable impact on PC performance. This software runs fine without any lag, etc. So, the actual video feeds seems to be fine and does not cause the card to put any strain on my PC.

I open up OBS and everything is fine. I can add a display capture and everything is still fine. No noticeable performance loss for OBS.

However, when I add my video capture device source, OBS begins to lag like crazy. I'm not even streaming and OBS is having a hard time running. The preview window is apparently only getting 20 FPS.

Any clues as to why OBS takes a dump when I add my capture card as a source? I can have preview enabled or disabled and it does nothing to help.

My stream itself does not appear to suffer. If I begin streaming, it runs just fine (the stream). OBS still lags but the stream doesn't seem affected.
 

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betawarz

betawarz

New Member
Yes, game mode is off.

Do you think it's the resolution of that capture device? It's a 4k video feed. I'm unsure of how or if I can down scale that prior to OBS using it. Perhaps OBS is choking on trying to downscale it itself?
 
Harold

Harold

Active Member
Your log isn't showing a downscale.

It's showing that you're overloading your video card somehow.

Screenshot of the first tab of gpu-z please.
 
betawarz

betawarz

New Member
My gaming PC's monitor is that 1440p resolution source. The streaming PC's monitor is 1080p. The capture card supports up to 4K resolution, but is paired with the 1440p monitor and so it should only be capturing a 1440p signal, or however that works. Maybe that clears up a bit of what you're seeing in that log?
 
Harold

Harold

Active Member
ok there's the problem.
Your video card is in pci-e x1

It NEEDS to be in x16

Either move it to pci-e x16 slot 1 or make sure it's seated properly in it.
 
betawarz

betawarz

New Member
@Harold the X1 slot has my Magewell capture card on it. The GTX 980 is in a standard PCI-E slot, as it would not fit in an X1 slot.

Maybe I should move the Magewell capture card to a regular PCI-E slot? I'm not sure if that works or not.
 
betawarz

betawarz

New Member
No, I believe it's in the 2nd PCI-E slot. The first slot may not fit, as the heat sync may stop it. I can try, though.

That GPU-Z screenshot also confirms that the 980 is in the PCIe x16 2. I'm not sure why it says @ x1 - perhaps it's for power saving since it's not in use?
 
Harold

Harold

Active Member
No. It doesn't decrease the number of lanes, only the pci-e version.

If it's in x1, it's NOT in the right slot.
 
betawarz

betawarz

New Member
@Harold hmm, OK. I didn't realize it had to go into that first slot. I thought any PCI-e slot would work. I'll make the swap and be back in about 20 minutes.
 
betawarz

betawarz

New Member
Holy cow. That actually fixed it. I had absolutely zero clue that the PCIe slot mattered. I don't even think my brand new gaming PC has its video card in the first PCIe slot. I'll be changing that too, lol.

Thanks so much for your time!
 
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