ROBERT SAYRE wrote in a message to ROY J. TELLASON:

RJT> WC> I've seen 1,000 hour camera tape machines advertized.

RJT> Oh really?  And these use standard tapes?  I wonder how they do that...

RS>  Usually they use a stepper motor that advances the tape one step, 
RS> pauses, then one more step, etc. This writes over the same spot on 
RS> the tape a few times. The last time being "saved" and then 
RS> advancing to the next step, pause, etc.

This is a modified VCR?

RS>  You lose frames, but you get a much longer record time. You get to 
RS> choose the speed, and therefore the number of frames to "throw 
RS> away".

Makes sense.

RS>  Better systems will monitor the video and only advance the tape 
RS> when a change is detected. 

That makes even more sense.  I've always suspected that video should be
seriously compressible...

RS> If no change is detected within a short time, the heads stop 
RS> spinning. When a change is noticed, the heads are brought up to 
RS> speed and the pictures are recorded from memory until the tape 
RS> recording "catches up", then they go on to the tape directly.

Hmm.

RS>  Even better systems will monitor several cameras in this way and 
RS> record only the ones where changes are detected. The cameras are
RS> recorded by time division, with memory saving one or two cameras as 
RS> another is going onto the tape. The memory is recorded during the
RS> appropriate time slices as the first camera goes into memory.

RS>  Camera "robots" can take this even farther by letting you decide 
RS> which part of a camera's "vision" to monitor for changes and how 
RS> big of a change must occur. They can also give presidence to one or 
RS> more cameras over all of the others. They can save more detail from 
RS> some cameras at the expense of all others, too. A typical robot can 
RS> control 16 cameras.

RS>  We currently use a computer system, with video going directly onto 
RS> hard drives. 

That's where my thinking was going next on this.  Aren't there a couple of
consumer appliances out there that use hard drives?

RS> It can (does) do all of the above and more (alarm by time of day, 
RS> access control camera call-up, playback during recording, etc.). 
RS> Our system currently supports 64 cameras, but we're building another
RS> six story section, so we'll be expanding this a bit.

Hmm.  Is this sort of thing real pricey?

It's interesting where this technology is going,  like the two local
competitive tv stations that each claim "exclusive" traffic
cameras, though they've both had them for quite some time now.  My brother
installed *all* of them,  in various locations.  Some of our conversations
about the hardware and what it can do are also pretty interesting,  though
I had no idea that the signal processing had gotten as interesting as what
you've described above.

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