Multiple inputs from 1 single BTTV card?

[gsbarbieri]

Hello,

It is possible to record multiple cameras from a single TV card? I mean, if I have 4 cameras, each one in its own channel (ch3=cam1, ch4=cam2, ...) or even only one channel that receives images from 4 cameras in sequence, 1sec between them (0sec=cam1, 1sec=cam2, 2sec=cam3, 3sec=cam4, 4sec=cam1, ...)?

The first solution would require a hw (which I don't know if exists) to get N inputs and put it in N channels. Maybe it doesn't work because the tuner is slow and would loose many frames.

The later is probably the easiest, but I don't know if it's implemented. The hw is available and you can even change the time intervals.


Thanks,

Gustavo

[pchan]

The easiest solution is to purchase a hardware quad video processor or video multiplexer. Multiplexers will allow you to cycle through the cameras at some designated interval. Quads will combine 4 cameras into a single image. Either solution will solve your problem of using a single capture card for multiple cameras.

[gsbarbieri]

Sorry, but I did mean the software support to it so using a multiplexer with 1/4 second interval between frames it would act like 4 independent cameras at 1fps each. The software would capture from one input (/dev/video0) but would report as 4 cameras in the interface.


Gustavo

[heyarnold]

Hey guys,

I think that Gustavo's idea is great, I was thinking about this myself. It seems other people were thinking about this too!

Please look in the request forum: http://www.zoneminder.com/forum_feature ... e15b3325dc

There are some suggestions there. I also have a magazine article in pdf format that shows how to build a switcher based on a Maxim MAX454 chip. The circuit uses a counter to automatically switch through the video channels. Of course the couter would need to be replaced with a simple parallel port interface to make it controllable by a computer. If anyone is intersted in trying to make this work I can e-mail the article to them.

[zoneminder]

One thing I have thought about in the past is to be able to switch between 'channels' on a single feed. By this I don't mean channels as in separate inputs but individual frequencies on a single TV tuner input where different cameras are represented as different stations. There's not really been a huge demand for it and I've not done any tests to see whether it is feasible and it may be that the switching time is too long for it to be of any real use but it might not be too hard to do in the software.

Phil,

[leop]

I'm using a video multiplexer to cycle between 3 cameras, and feeding to a BTTV card. Are there any suggestions as to how to configure zoneminder to monitor video like this? Since its changing every 4 seconds (longest interal the multiplexer allows), wouldn't that totally fubar any event/motion detection, and create thousands of events/images? I'd like have zoneminder watch this input, and possibly record about 14 hours a day at maybe 2 fps, but I'd also like to do it without filling my HD every day, and have the resulting data be usable/viewable in a practical manner. Any suggestions?

[gsbarbieri]

Phillip,

The time tuner takes to change may be big, as you said, but you have 2 options yet:
- Use 2 cards, when you record from one, you change the channel in the other, then when you stop recording from the first, the second will be available already. Imagine RISC pipelines.

- Use only one card wich receives the input from a multiplexer which is time based or controlled using parallel port by zoneminer. The switch will be fast, since you don't have to tune in frequencies, just change from which cable the source comes in.

Gustavo

[lazyleopard]

One approach might be to have some sort of pre-screening of frames, but this would up the load on the CPU. A coarse-grained fingerprint, when compared against a table of fingerprints of known sources, can be used fairly successfully to determine which of N possible cameras a given frame came from. Not quite sure yet where such screening might fit in the ZoneMinder scheme of things, but there's a GPL-ed perl script called "findimagedupes" that uses a technique of this sort based on functions in Image::Magick.

[andrewgroup]

I think this would result in synching troubles. The software would require an external input to indicate when the switch was to occur. I also think many of the multiplexors have lower limits on the speed at which you can rotate among the 4 cameras.

[lazyleopard]

The switching unit I have holds each camera for (at most) a bit over ten seconds. Then there's a switch over where a frame or two may be a mixture of two images, or some mis-sync, followed by several frames from the new view where the frame grabber struggles to re-adjust to the levels from the camera. This messiness at switch-over means that too quick a cycling of cameras would render the input completely useless. Trickiest bit would be knowing what is dross that needs discarding.

[zoneminder]

My preferred option for muxing multiple inputs together would be to RF encode them on separate frequencies and then effectively change TV channel between them. Having said that ZM doesn't currently support that (as there's been little demand) and I dont know how quickly such a switch would take place. It's a little less Heath Robinson that trying to time switching though.

Phil,

[lazyleopard]

Timed switching units are quite common (and therefore reasonably cheap) in non-computerised multi-camera systems. My gut feel is that multiple video cards is the way to go for computerised systems, where it's practical, though.