Q: Is it possible to connect a keyboard for input to DVR and NVR?

No, it's not supported.

The 2MP DVRs allow input and operation through a mouse and remote control.

For the 5MP hybrid DVR/NVR, POE NVR, and 2MP WiFi NVR, input and operation are limited to a mouse.

For all the TIGERSECU DVRs and NVRs, wireless mice are also compatible.