Best way to stream 4K gameplay with a single PC and a capture card?

Hey! Great question. With a single PC and that beast of a CPU (i9-13900K), you can definitely stream 4K without a capture card—just use OBS with NVENC. The RTX 4080 has the new NVENC encoder which is excellent and offloads encoding from the CPU, so you won't see much performance hit. For 4K streaming, you need to be realistic about bitrate. YouTube supports up to 51 Mbps for 4K, but Twitch caps at 6000 kbps (which is too low for 4K, so you'd have to downscale to 1440p or 1080p there). Since your upload is 20 Mbps, I'd recommend streaming to YouTube at 4K with a bitrate of 20,000 kbps—that will give you a crisp image. In OBS, set your base canvas to 3840x2160, output to 3840x2160, and use the NVENC H.264 encoder. Make sure to enable 'Look-ahead' and 'Psycho Visual Tuning' for better quality. For the capture card, you don't need it for single PC streaming—it's only useful if you had a second PC. You can use Display Capture or Game Capture in OBS. Just test it out, but I think you'll be fine!

Absolutely agree. To add to that, if you're also considering using x264, with your i9-13900K you could use the 'veryfast' or 'faster' preset at 4K, but it will use a lot of CPU and might cause frame drops in-game. NVENC is the way to go. Also, make sure your OBS settings are optimized: set the 'Keyframe Interval' to 2 seconds, and use 'CBR' rate control. On YouTube, you can stream at 4K60, but if you want to save bandwidth, you could stream at 1440p60 and upscale—YouTube will still show it as 1440p, which is better than 1080p. But since you have the hardware, go for 4K. One thing: your upload speed is 20 Mbps, so 20,000 kbps is exactly the cap. You might want to leave a little headroom to avoid network spikes, so maybe 18,000 kbps. Also, check if your router supports QoS to prioritize streaming traffic. Good luck!

Thank you both for the detailed replies! I decided to go with the NVENC encoder as you suggested, and after tweaking my OBS settings to 4K at 18,000 kbps, the stream looks fantastic on YouTube. I also disabled the capture card idea—it wasn't needed. My game runs at a solid 60 FPS with no dropped frames. I really appreciate the help!