I worked with some of them years ago and they had plain PAL/NTSC inputs which are low res, but more recent models should be all AHD compatible, which is hi res albeit still analog. The standard was created by Korean company NextChip.

https://www.nextchip.com/en/ahd/ahd.php

https://en.wikipedia.org/wiki/HDcctv

edit: just found some data about a manufacturer of high res video sampling chipsets, along with some open source software for them.

https://www.unifore.net/product-highlights/nvr-dvr-hisilicon...

https://github.com/openhisilicon

Hmmm, thanks. It seems AHD 1 is 720p30 and AHD 2 is 1080p30, but basically just plain yellow RCA jack (just, well, overclocked accordingly). Usability as SDR depends on how well the genlock can be turned off, and how well the h/v blanking can be eliminated. One of them, the NVP6114, seems to have a COLOROFF_x register and a selectable color kill mode (no Y/C separation vs. after Y/C separation). The no-separation + color kill seems to be the closest to dumb ADC, if genlock can be eliminated. AGC seems to be somewhat optional.