Nintendo Maniac 64
Your video is anamorphic.
In pixels it has size 900x600, but this picture has aspest ratio 4:3.
So if your screen has resolution 800x600 then one side of video must be equal, second side must be less. I think so because SD 720x576 with 16:9 flag gives at output 1024x576. (upscale 720 to 1024).
If we go with this logics then we need to get 800x5xx from 900x600 source to get stretched frame to 800x600 at the screen. And if I use madVR I see this logics working.
But with EVR I see another logics and 800x5xx shows me black bars as at your picture.
I must say it is not simple situation. Two different renderers work in different way: madVR used upscale, EVR used downscale.