The Problem:
When using capture cards on my PC to capture a games console or to capture my PC via monitor cloning, I get intermittent video stuttering in the capture, even though there is no stuttering on my monitor through the HDMI passthrough or monitor being cloned. This happens in the video preview without recording or streaming. In OBS, there is no rendering or encoding lag showing in the stats.
See these two videos (watch them in full screen):
Stuttering Video When Capturing Games Console:
https://www.youtube.com/watch?v=bzT3Fi4_ulM
Stuttering Video When Capturing Cloned Display:
https://www.youtube.com/watch?v=Ro-j5T-5UJQ
I initially thought the cause was my Elgato 4K60Pro MK.2, so I bought a different card—a Magewell Pro Capture HDMI 4K Plus LT—but the exact same problem persists with this capture card, too, ruling them out as the cause. I've tried both them in both PCIe Slots 3 and 5. Problem persists. (Slot 1 is populated by my GPU, and Slots 2 and 4 are only x1—forget about them. Slot 1 is PCIe 4.0 x16, Slot 3 is PCIe 4.0 x8—which when used, drops Slot 1 to x8—and Slot 5 is PCIe 4.0 x4. That is: x16/x0/x4 or x8/x8/x4. Slots 1 and 3 use the Ryzen CPU lanes, and Slot 5 uses the X570 chipset lanes.)
I normally have my Focusrite external audio interface plugged into a Thunderbolt 3 add-in card (a Gigabyte GC-Titan Ridge V1), which is plugged into PCIe Slot 5, so I tried disabling Thunderbolt in the MB's BIOS. Problem persists. I've even tried plugging the capture cards into an external PCIe to Thunderbolt 3 external enclosure (a HighPoint RocketStor 6661A), and plugging that into the TB card (in PCIe Slot 5). Problem persists. I've tried three different MB BIOSes (ASRock X570 Taichi BIOS versions 3.40, 3.00, and 2.70). Problem persists.
I've tried OBS, VirtualDub, Elgato 4K Capture Utility, and Magewell Capture Express. Problem persists. I've tried the x264 and new NVENC encoders, and various settings, resolutions, and frame rates in the softwares. Problem persists. The exact same video stuttering shows in all programs, whatever the settings are. As I said in the beginning, this happens whether I'm capturing a games console or I'm capturing my PC (in a single PC setup via duplicating my desktop).
I've tried turning off my GPU overclocking software (MSI Afterburner). Problem persists. I've tried disabling my second and third monitors. Problem persists. I've tried disabling G-Sync and messing with various other settings in Nvidia Control Panel. Problem persists.
I've updated Windows, all my software, drivers, firmware, etc. Problem persists.
Other than all this, about the only thing that I haven't tried out is throwing my PC out of my window! As I've already said, this intermittent video stuttering only shows in the capture; it doesn't show in the HDMI passthrough to my main monitor.
So, I've ruled out the capture cards, having Thunderbolt enabled in my BIOS, the capturing softwares and their encoding settings, and a dodgy motherboard BIOS. My CPU and RAM seem to be working well (they pass all tests in Memetest86). And my GPU seems to working well (no crashing or glitching in testing and playing intensive modern 3D games). I plan on upgrading my GPU to an RTX 3080 or 3090 soon (when I can get a hold of either one of them), which are PCIe 4.0, which my motherboard supports, so I'll see if that changes anything.
Anyway, what else could possibly be causing the problem? Could it by the motherboard? Everything else in my system works fine, including my Thunderbolt add-in card and audio interface when plugged into PCIe Slot 5. Could the motherboard be incompatible with capture cards??
My system:
Motherboard: ASRock X570 Taichi
CPU: Ryzen 9 3950X
RAM: 64 GB 3600 MHz HyperX Predator
GPU: MSI RTX 2080 Ti Gaming X Trio
Other PCIe card: Gigabyte GC-Titan Ridge V1 (Thunderbolt 3 add-in card)
Audio inferface: Focusrite Clarett 2Pre Thunderbolt (audio interface)
PSU: Corsair RM1000x
I've also posted about this in an oldish thread on the Linus Tech Tips forums here (beginning from the third post down), where two other people seemed to have had the same problem:
Hi, I'm trying to track down the source of some intermittent frame stutters on my capture card. When recording 1080p60 content, the recording will occasionally act like it's dropping frames, even though the capture or streaming software reports no such thing. It's hard to describe, but it's like ...
linustechtips.com
If you read my posts there, you'll know that because of this problem I've gone insane and I'm now living in the woods. O_O Please get me out of the fucking woods. Someone. Anyo
This is just trolling now. Goodbye.
I have the same problem as you, I tried to do tests on other computers and the same thing happened to me and I already discovered what it is, the problem is caused by the RTX graphics cards, try any other that is not from that series and you will see that the stuttering will disappear completely, I tried a laptop with a GTX 1070 graphics card and it runs super smooth, try to try another video card that is not RTX and you will see that the stuttering will disappear (sorry for my bad english)