capture cards are devices primarily intended for game streamers to give your computer an hdmi input to stream/record games from a game console, but are also useful for other purposes such as turning your dslr into an expensive webcam.

i have this one: https://www.elgato.com/en/gaming/game-capture-hd60-s-plus

you can find others from magewell

i don't have measurements but the latency was indistinguishable from a directly connected webcam.