Spilt Final video

[MattGamingV1]

I was upscaling demon slayer from 1080p to 4k But when it finished It was split into 3 parts (I used the Vulkan option for this process.) Is there a way to disable this? Also Its not taking advantage of my GPU (RX570 8gb) probably because Its AMD and doesnt have CUDA but i was wondering if theres a different option to make it compatible albeit slightly unstable.