It seems like AVtech 4ch network DVR has a video server software that can be used by multiple users over the Internet to watch or control CCTV cameras.

The problem is that AP software requires Windows XP or 2000.
I'm not an expert in Macs or especially in stream broadcasting on Macs, but IMHO the simplest solution is to run Windows on a Mac using software like Bootcamp or Parallels Desktop for Max OS X.

If you somehow can get videos or images on your Mac from AVtech 4ch network DVR, you will be able to send them over the network. You can say use freeware Videolan. However there could be problems with time delay, starting a broadcast from a remote computer,...