I think there is... We all seem to be on the same subject, same ideas, but different implementations causing different discussions.it sounds like there is a little misunderstanding on what everything does.
If the computer doesn't record, just displays a live view, no audio on pc side either, I don't think the hit would be enough to notice. Now, the dvr, or dvr with built in multiplexer would do all the recording. This leaves the pc to not have to worry about recording, yet we'll still have recordings that can be accessed via dvr. I think this sounds right.it really depends on what the pc is doing-- in most cases, letting the pc "do it's thing" the hit that this takes will be very minimal. some of my customers have complained of a very slight audio echo from this process-- i would have to guess it is in the 100-200milli-second range-- not huge, but enough to be a tiny bit behind.
but if you have a kid in back playing a video, it could become a big hit, and could slow down how fast the live view gets updated(if the pc normally recorded at 30fps, but might drop to something like 10-15fps).
but this also is dependent on the capture card that you use. some do a very good job encoding the camera signal, to the point that the cpu is barely needed, others really rely on the cpu for encoding...
Leaving headlights on overnight is never a good thing... Even with today's batteries I've done it and never had an issue, but if these are left on all the time just in case motion sensing needs to record something, this could cause huge issues. Since you've worked with cameras and dvr's before, have you ever worked with the motion sensing? If the cameras stay on with little power draw, is there a different wire, voltage, etc that comes from the camera for that detection? If there is, a simple relay could be triggered to power the dvr back up until the motion sensing/recording is done... Maybe we're crossing discussions again, it's a lot to learn .overall, for 4 cameras and a dvr, your talking about 400mA + 5A, so about 5.5A draw-- less then a set of headlights.