Hi Koala, THANKS for the big effort to respond in such detail. If you want all 3 monitors combined in one big video, you need to take a different approach which involves downscaling the original monitor images, but keep in mind that if you want this, it will probably be very difficult at playback to see all the chart details in the downscaled video. After a few minutes, stop recording everywhere and verify the resulting videos. Switch to a different scene in each of the running instances of OBS and start recording, so you're recording all 3 monitors with your 3 different running OBS instances at the same time. It will complain that it is already running, but ignore this message for now. If you're satisfied, start OBS two times more. Try to record one of these scenes for a few minutes and verify the resulting video. Now you should have 3 scenes and see the corresponding monitor in the OBS preview if you switch to the corresponding scene. Now set up 3 scenes in OBS, each with one 'Display capture' source and point each to a different monitor. In Settings->Video set 3840x2160 for both resolutions and 15 or 10 as fps value. Since you're recording desktop and charts only, the size increase is probably not very high actually. If you find the quality isn't good as you need, choose 'Indistinguishable Quality, Large file size'. In OBS, use simple output mode, and as recording quality set 'High quality, Medium file size', mkv as recording format and 'Hardware (NVENC)' as encoder. Since you're recording a desktop with emphasis to text and chart, not to animations, you can lower the fps to 15 or 10 in OBS to reduce the amount of data to encode.

Note that Nvenc is able to encode only up to 4096x4096 with x264, so you need 3 recordings in parallel, each of your monitors separate.

Relevant is the 'Max # of concurrent sessions'. If you have a reasonably recent Quadro card, you have Nvenc as encoder, which is essential in this case. Live encoding 3x 4k is extremely resource intensive, even if it is 'only' charts and no real video like gaming or camera.

Snagit screen capture 4k