https://www.hikvisioneurope.com/eu/portal/portal/Technical%20Materials/02%20%20NVR/00%20%20Product%20Firmware/05%20K-series/05—76%2077NI-K2%20K4/V4.74.200/NVR_K51_BL_ML_STD_V4.74.200_230522.zip
V4.74.200