How does OBS work hardware wise? Will an older cpu create input lag?

[Perraddidle]

Hi, I have a dual PC setup. My capture card is an Elgato 4k 60 pro mk2, It's receiving a 1440p 144hz signal from a cloned Samsung g7 set to 240 hz.

The capture/streaming PC has 16 gigs of ddr4, 2933 mhz, an i5 8500 cpu and a Gtx 1660 gpu. SSD hardrive.

If I game without OBS on everything is great. If I open up OBS, I get input lag on the gaming pc, even though it's not running OBS. It;s only connected to the capture PC with 1 HDMI. I'm not doing passthrough, just input to the 4k60.

I get less input lag if I shut off the preview window, even less input lag if I minimize OBS and don't have it open on the screen. But there is still some compared to not having OBS running.

This fries my brain as a dual PC setup should eliminate issues like this. I wonder if it because the CPU is an older i5 8500. It's also the same when I use nvenc on the 1660. In fact I always use the nvenc new.

Does anyone else have this kind of issue?

 

[Lawrence_SoCal]

Starting OBS causing the computationally demanding real-time video rendering work to begin (if in a Source, even if not currently displayed). Using Studio Mode = 2X rendering workload. So, yea, LOTS of threads about PC impact when starting a often very demanding workload as OBS can be.

not my area, but as no one else has responded, here are some things for you to check
- No game play on gaming PC impacted by running OBS on PC#2? that's odd... BUT.. you mention very high screen refresh rate and a capture card at a MUCH lower (1/4) refresh rate (or??) .. So, maybe OBS doesn't have anything to do with it? maybe hooking up the capture card and rendering to a 2nd display output (with different settings than main gaming PC monitor)? or maybe a gaming PC video driver driven impact?
- to eliminate OBS as cause on impact on gaming PC... have you tried using some other screen capture/recording s/w (like native Windows Recorder) just to test impact.. it maybe that when starting capture, signal sent to Elgato, and that is adjusting refresh rates?
also, I'm not sure I follow 240hz and 144hz? I would initially think you have a monitor on gaming PC that can run at 240hz, right? why send a 1440p144hz signal to ElGato? if that what it recommends? common recommendation from those that know WAY more than I is to keep frame rates, screen refresh, etc as simple multiple of each other. So if doing 60fps, maybe set screen refresh to 120hz?

 

[Perraddidle]

I have a 240 hz 1080p monitor and a 1440p 240hz monitor for gaming.. I tried having 240z 1080p for both the gaming and streaming pcs. I still got the same amount of input lag on the gaming pc. Currently I have a 60 hz for streaming pc. 1440p 240 hz for gaming and it's being sent to the Elgato at 1440p 144hz as a clone.

I've tried using OBS to do a projection to the elgato at 60 hz as a second monitor. Same amount of lag maybe more as there are 2 OBS's open when doing that.

My theory is that the Elgato has to use the Cpu and Gpu to generate the video input coming in. OBS also uses the same cpu and gpu to create it's newer version of the video with overlays/webcams etc. Along the way there is probably some kind of video handshakes that the HDMI from the cloned signal from the gaming PC, OBS and the streaming PC monitor have to agree on.

I'm not sure if it's because my streaming PC CPU isn't hyperthreaded and only 6 cores, Even though with everything running by CPU only hits 40 to 50 percent max. Chrome uses more resources than OBS. My GPU is only running 11 to 12 percent. Maybe that's a maxxed out Nvenc chip, I dunno.

Does an nvidia Nvenc chip have the same amount of encoding power regardless of the type of GPU? Will a 2080ti be better than the current 1660? Sometime this week I will build a rig with a i9 9900, and a 2080ti and see. I wish I could put the 2080ti in the same machine replacing the 1660 to see but the case wont fit it.

 

[Perraddidle]

Ok, I have tried a few things and an Epos Vox video where he tests using a lower end PC vs Higher end PC testing HDMI passthrough makes latency, makes me think newer gear might make a difference.

When I changed the CPU Priority to real time, it created less input lag. This leads me to believe that a combination of the CPU and GPU are taking in the signal from the Elgato and producing the video stream. The video stream is going to have a place in the queue of what is happening on your computer and making it a first priority makes a difference. I'm not sure you want to do that on one PC but it might work depending on what you are doing and your gear.

Since the CPU and GPU are the ones responsible for creating the stream and it it time sensitive, despite the nvenc chip being the same. Actually I don't know if the Nvenc chip is a physical thing or just a process that gets updates over time. I haven't seen anyone say that a 4090 has a better nvenc chip than a 1660. What the new nvenc turing version circa the 20 series does is it keeps the process inside the ram of the gpu. So in theory if you have a GPU with better vram latency like ddr6 or ddr6+ it might give you better input lag. The 1660 has ddr5.

Also a CPU with larger cache might reduce the latency as it will have more resources for things that are a priority.

So given my assumptions, switching to a i9900 vs a 8500 and a 2080ti vs a 1660 should give me better input lag. But perhaps the difference can't be percived. I dunno.

 

[Perraddidle]

Ok, so I bought a new power supply to handle the 2080ti, I had a 500 watt non modular Seasonic and switched to a Corsair Rm850x.

That was the only change I made, so still an i5 8500..There was an improvement. I did notice that disabling the preview window and minimizing OBS reduced the lag just like before but the starting point was way better. It had less input lag that with the 1660. Also visually it was much clearer.

The only other minor change was the monitor that was attached to the streaming PC was HDMI instead of display port to HDMI adapter. I use the streaming computer for College work and use the gaming monitor as well as the streaming monitor.T

the 1660 only has 1 HDMI and 1 Display Port. With the 2080ti I can have both be HDMI instead of display port to a HDMI adapter. I don't know if that makes a difference. When I was gaming and streaming with the 1660 the streaming monitor was a display port to HDMI adapter.

Next I will replace i5 8500 with an i9 9900 and see if that helps as well.

 

[Perraddidle]

Ok, I swapped out the 8500 for a 9900. I'm not seeing much of a difference in input lag. One other thing I'm going to do is change the OS drive to a Samsung evo 970 ssd from a 40 dollar Kingston ssd drive. There seems to be alot of data transferring from the drive when OBNS is running.

 

[Perraddidle]

Ok, so after installing an new OS on a Samsung evo 870. I didn't see an improvement there.

The biggest improvement for me was switching to a 2080ti from a 1660. I also switched the power supply from a 500 watt Seasonic S12 to a Corsair RMX 850. The power supply in my Gaming rig is a Corsair Hx 850i.

I did see a clarity improvement and lower input lag of my gaming monitor in general. It could be because of the upgrade to the 2080ti, or perhaps it was the extra juice power supply wise or maybe they coexist better as the new power supply setup are both from the same manufacturer. I don't know if different power supplies in pcs that are linked via HDMI could cause an issue.

The clarity improvement could also be because with the 2080ti was able to send out an HDMI to my streaming monitor. Previously it was a display port out to an adapter to HDMI on the monitor. I'm not sure if blending HDMI and Display port can cause issues performance wise in regards to input lag. For most people they wont notice any of this at all. Another thing I noticed is with the 2080ti vs the 1660 on the streaming PC alt tabbing out of a game was a different experience with the game getting smaller in a lack border outline. It's like it had a different full screen exit vs the 1660. Maybe I wasn't in proper full screen mode on the 1660.

So my advice for dual streaming PCs for the maximum clarity and input lag reduction is to get the same manufacturer of power supply for both PCs. Get the best GPU you can afford for the streaming PC, make sure your monitor outputs on the streaming PC are HDMI to coincide with the HDMI coming into the capture card.

Another thing that helped alot was to set the CPU priority for OBS to real time. Disable preview window and minimize OBS.
Each one of those steps reduced input lag on the game I was playing.

I still have no idea how OBS on a streaming PC can effect input lag on a gaming PC but it does. This has been my adventure in trying to figure it out. For me I haven't been able to eliminate it completely, just reduce it alot.