After being told several times that I could do this, I have ordered a doorknox vdp102 and it's relay box from SystemQ to tie in with a megahero dvr from them I already installed.
It has video, audio and alarm signal out to the dvr so that you can see and hear the front door, and recieve a notification when the button is pressed. The problem is that, despite the vdp having a speaker, you cannot talk back to it from the dvr. Their tech told me that the single audio cable only works in half duplex from their monitors. He wouldn't reveal a way to go around this, instead they want to push their voiceoff unit which would do the job, but is an ugly thing above a front door and a waste of money when the vdp has a built in speaker.
Does anyone have any ideas? I'm assuming if I wire both dvr audio in and out with some diodes that the vdp will automatically switch to speaker mode when detecting an audio output. This is starting to get beyond my expertise, but I already have the job booked in after their sales chaps misinformed me.
Alternatively, are there any other door entry cameras that can be wired up to a dvr this way? All I can find now are the wifi units which have their own apps. Aperta wifi looks good, but can you access the video stream over ip so that the dvr can record it? Any others that you can?
Many thanks