Halo 2 640x480 with 16xSSAA
This was rendered at 5120x3840 (That's ~2.4x more than a native 4k resolution) then downscaled to 640x480 and losslessly captured.
It was then losslessly upscaled through FFmpeg to 2880x2160 (non-integer) with a nearest neighbor filter to be YouTube friendly.
Achieved with ValveSoftware's GameScope for Linux. Special thanks to @RuanEvangelista