If you have more cameras than DVR channels, have people found it useful
to use some sort of interleaver that will toggle rapidly back and forth between
two cameras? Obviously, motion detection on that channel will be useless.

I assume the other choice is a "combiner" that will reduce the size of each
image and stick them together, with a resultant loss of resolution.

Is there any device that will combine the top 1/2's of two camera images
to form a new image? In my application that might work since my window
is not so high but wide. I suspect such a device would be super expensive.

Standard multiplexor will do all that. The VCR output of a MUX typically just flips quickly from one view to the next, synchronized to the video fields recorded in each pass of a helical-scan VHS head. You could feed that into a DVR and get alternating views of each camera - the quality would probably suck, but it would work.

Or you could take a 2x2 or 3x3 or even 4x4 grid main-display output of a MUX and feed that into a DVR channel - each portion of the image will be tiny, of course, but it will work as well.

We did have one site where there was one camera run going to the gas-pump canopy and they wanted two cameras, so someone (before my time) added a simple video switcher *inside the canopy* to toggle two cameras over one feed into the store. It was painful, because the view usually flipped just as you go to the part of the video you wanted to see.

yes you can do it, one version is called a quad
does work most times, tho as you say motion detect mode will be no good.
they are not expensive >ok for general overveiw only.

you can even put a quad into a quad ! but the images will get small

DVR cards are cheap these days !

A quad would be your best bet, half screen splitters usually needed genlock (whats that, I hear the new guys asking... better that you don't need to know anymore!)

This one makes me nostalgic for an install I did years ago that used two Robot muxes.. One encoded for both the recorder, and split off through a single twisted pair link to get demuxed at the far end for viewing..Ahh, the good old days..NOT!

Just joined the forum, so only now caught this question.

There is a specialist product for this application made by Ovation Products in the UK.

Hope this helps.

Ilkie

Thanks, ilk, I found a product on that website, called "micro-foursight" that's basically perfect for my application.
It will crop & combine two images into one without any scaling, and it only uses 150mA.

Only two problems:
Do they have any USA resellers?
The device has 4 inputs, but only one output. I need the four inputs, but two outputs so I can do two separate "joins".
I.e., two 2-joins rather than 1 4-join. Is there any product that does that?