1080p is not enough. And to avoid losing quality by the scaler I would how said recommend to upscale without interpolation (nearest neighbor) by a factor of x2.
Then you end up with 1600x1200 (if your game is 800x600 (never heard of 800x500, you can only mean 800x600).
1600x1200 gives you the minimum of 1152pixel to reach youtube's ID 308 encoding, which is the one for 1440p videos and has 10000 kbit bitrate, while ID 303 (1080p) has just 3500 kbit and 1080p looks totally crap on youtube. An artifact nightmare.
PS: Windows Timeline Software has terrible Scaler and terrible decoder and terrible encoder. Thats why it can read only h.264 files with a chroma resolution of 4:2:0.
Your next problem is, that lossless needs the high444 predictive profile of h.264. Another stuff Windows Timeline Software cant read...
The only software with slightly better support is TMPGEnc VMW 6 (which even has x264 and even can read mkv and output mkv and has more than 3 settings for the encoder)
And Shotcut may read in some more formats due to its ffmpeg implementation.
Colormatrix of 709 will work with vegas too though.
At OBS you have no nearest neighbor scaler, just interpolation ones (bilinear, bicubic and lanczos). And interpolation takes some cpu. I would recommend to upscale the video afterwards anyway because also for the x264 cpu usage it is recommended to do the upscale afterwards, because then x264 has to process just 800x600 pixels and not the upscaled bigger frames.
Also I wouldnt use 1920x1080 as a scaled result, because it will stretch your video and that may look bad.
Then you end up with 1600x1200 (if your game is 800x600 (never heard of 800x500, you can only mean 800x600).
1600x1200 gives you the minimum of 1152pixel to reach youtube's ID 308 encoding, which is the one for 1440p videos and has 10000 kbit bitrate, while ID 303 (1080p) has just 3500 kbit and 1080p looks totally crap on youtube. An artifact nightmare.
PS: Windows Timeline Software has terrible Scaler and terrible decoder and terrible encoder. Thats why it can read only h.264 files with a chroma resolution of 4:2:0.
Your next problem is, that lossless needs the high444 predictive profile of h.264. Another stuff Windows Timeline Software cant read...
The only software with slightly better support is TMPGEnc VMW 6 (which even has x264 and even can read mkv and output mkv and has more than 3 settings for the encoder)
And Shotcut may read in some more formats due to its ffmpeg implementation.
Colormatrix of 709 will work with vegas too though.
At OBS you have no nearest neighbor scaler, just interpolation ones (bilinear, bicubic and lanczos). And interpolation takes some cpu. I would recommend to upscale the video afterwards anyway because also for the x264 cpu usage it is recommended to do the upscale afterwards, because then x264 has to process just 800x600 pixels and not the upscaled bigger frames.
Also I wouldnt use 1920x1080 as a scaled result, because it will stretch your video and that may look bad.