S-video is not good enough to submit here. For Dreamcast it must be using at least a good quality VGA box or the retrotink VGA dongle
https://www.retrotink.com/shop/hd15-d...-dreamcast along with an HD15 cable which may require an upscaler to connect to a capture card.
Otherwise an HDMI modded dreamcast (not just a dreamcast to HDMI cable as tests from those are usually rather poor) can be used too, like the retrogem for example
https://www.pixelfx.co/product-page/d...ro-gem-kit