It appears, from following RetroGaming forums that the reason the Pi4 and maybe Pi5 have hiccups with NTSC is that the GPU governor is dynamic, which maybe isn't a problem with HDMI pipelines, but Analog Video is very timing sensitive.
This needs to be tested and then added to the wiki.
https://ttt.io/glsl-raspberry-pi
# Required: Enable the firmware/fake DRM/KMS VC4/V3D driver
dtoverlay=vc4-fkms-v3d
# Optional: Increase the memory reserved for the GPU
# 16MB disables certain GPU features
gpu_mem=64
# Optional: Avoid GPU down-clocking below 500 MHz that slows FPS down
# Should be set to 250 on the RPi 3
v3d_freq_min=500
raspberrypi/linux#3935
It appears, from following RetroGaming forums that the reason the Pi4 and maybe Pi5 have hiccups with NTSC is that the GPU governor is dynamic, which maybe isn't a problem with HDMI pipelines, but Analog Video is very timing sensitive.
This needs to be tested and then added to the wiki.
https://ttt.io/glsl-raspberry-pi
raspberrypi/linux#3935