HD-CVI Quad Multiplexer

is it possible to use a multiplexer or a quad with hd-cvi and if so any suggestions

Dahua HD-CVI Ultra - 1080p models have a second BNC out that can be sent to the quad or mux.

Dahua make a device with 1 HD-CVI input, 1 HD-CVI output and a range of other outputs including composite video, VGA and HDMI.

You would require 1 of these devices per HD-CVI camera which would allow you to connect a composite output of each to a Quad or Video Multiplexer.

Note, some of the Dahua HD-CVI recorders have an additional matrix monitor output that allows an independent multi camera display of nominated cameras separate to the main local monitor.