Question / Help Advantages/Disadvantages of using SLI/Crossfire/Dual graphic cards systems for Encoding

[paddydj]

Hi there.

I've been trying to find a thread about this question. But I couldn't so I've opened this one here.
Currently I'm using:

- 3770k OC to 4.5
- GTX 680 slightly OC'ed / 2048
- 16g RAM
- A few SSDs

I'm mostly playing CS:GO on full hd which is no problem as long as the encoding resolution in OBS is set to 720p60 while using NVENC. I found that using GPU encoding will give better performance inagme than using x264 no matter what other
settings are being compared to. So with my CPU, NVENC is the only option for me to get satisfying results.
For the future I'm planning to get my stream working with 1080p60. Using either x264 or NVENC though for this resolution is quite perfomance heavy. While 720p60 results in a 40 frames drop (from e.g. 300 to 260 in CS:GO) recording in 1080p60 results in like 50% performance drop and weird jitter. SO:

My idea was to get another GTX 680 to let one card do the job on rendering the game itself and one card to just encode with highest quality and lowest bitrate possible. It would be nice if ppl who are using such systems would tell their stories about them. I'm wondering e.g. if one should acitvate sli or not. My understanding of SLI is, that the two cards will act as like one in most cases which will of course NOT result in doubled fps. But there's obviously a difference between using two GTX 680 in OBS with or without SLI.

So I'm asking, will another GTX 680 do this job so I can finally use 1080p60 without that big performance drop.
Thanks in advance!

 

[Videophile]

SLI does not work how you think it works in regards to OBS.

Only one card can be used in OBS, and thats the main card(The one your game on, etc).

To use 1080p60 NVENC, you might need to upgrade to a kepler GPU, like a GTX 970, 980, or 750ti.

 

[paddydj]

How sure are you about that only the card that the game is on can be used in OBS to encode?
Actually I'm already using two cards if i like, which is the GTX 680 and the OnboardGPU iHD4000.
The GTX 680 renders the game and the OnboardGPU is encoding. The problem that I'm encountering
while recording via Quick Sync is the more than visible loss of quality if I'm encoding lower than 10.000 kbps,
which is why I prefer NVENC over QuickSync to encode for streaming purposes. For HDD recording I'm using QuickSync over NVENC because at higher kbps like 20.000 (it neither uses the 680's GPU nor CPU) it creates super high quality video even at 1080p60 with pretty much no performance loss.

So I wish just to have the same setup with two 680's instead of one 680 and the onboard GPU so I get better quality at lower kbps.

 

[Videophile]

That's interesting, because the Quick Sync should have better quality at the same bit rate as NVENC.