Re: video capture methods

[Nigel Orr <Nigel.Orr@xxxxxxx>]

At 06:48 08/09/00 -0400, you wrote:
>My need is really to be able to capture images when motion is detected
in
>the driveway or at the front door.  So ideally, I should be able to
capture
>an image from any camera based on which motion detector saw motion.

My system uses composite video, PIRs, Comfort, and 2 relays, feeding a
Hauppauge WinTV card in a PC.  If an appropriate movement sensor is
triggered, Comfort selects the nearest camera and switches it through to
the distributed video wiring in the house.

There's currently 2 cameras, so one relay 'chooses' the camera, and the
other passes either the chosen camera (if the system is armed, or movement
is detected when it's disarmed) or television video (if the system is
disarmed) to the video 'bus' (which is currently all passive).  Once I get
a UCMDEV (and a spare evening!), the motion detection software will be
started when Comfort is armed, to avoid loads of photos when there's
'normal' tv broadcast video going through the system.  Currently I have to
start and stop it manually.

The motion detection software sees the sudden change when cameras switch,
and captures the current image, and any subsequent motion while the motion
detector is still being triggered.  After a few seconds, Comfort switches
the output off again, so it 'falls back' to a camera covering a wider area,
where PIRs would be inadequate, so it detects motion from the picture
alone.

> 1) modulate all cameras onto their own channels.
>2) feed this signal to video capture card.
>3) when motion detected, change capture card tuner to desired channel
and
>capture.

You could do it that way, but it would reduce the picture quality somewhat
(by modulation and demodulation), and, IMO, would be more complex (as
you've noted)

>The 3 challenges I can see right away are 1) how to change the capture
>card's channel and 2) how to make sure the saved file gets a new name
each
>time, or somehow does not overwrite the previous file in case I have
not
>gotten it yet, and 3) how to tell the card to capture.

Dunno about all those, they are probably handled by commercial Windows
motion detectors.  Mine runs under Linux, timestamps pictures and saves
them as JPEGs with a name devised from the capture date and time, then
produces MPEGs of sequences if required to save space.  Mark can probably
post details of his Windows system which ISTR does much the same job.

>software that detects motion from the camera's image changing, maybe
this is
>the way to go?  I'd really prefer the first option as it would allow me
to
>capture an image whenever *I* wanted to, not whenever the *SOFTWARE*
>wanted to.

With my system, if you want a picture, just switch to that camera, the
sudden change will fool the software into thinking there was a big
movement, and it will store a picture.  I'd initially thought that would be
a disadvantage, as I was planning to cycle continuously through the
cameras, but it's now a 'feature' , as there's only one which doesn't have
a linked movement sensor :-)

Hope that helps,

Nigel