@jmcdra said in If one were to install mednafen on retropie...:
I'm also noticing this input delay on RetroArch too
You should have started from there instead of making it look like a mednafen issue. In the first place, i can hardly make sense of using mednafen standalone to play nes games on rpi4, there are plenty of better options afaik.
Retroarch has the P+K method to measure input lag, and in my experience the nes cores usually have 0 frames of input lag (i.e. the game reacts at the frame right after pressing a button), there might be exceptions but i doubt it ever goes beyond 1 frame.
If you are experiencing huge input lag on nes emulation, then i can only suppose something unrelated to emulation is at work here, like display lag or something about your controllers.