[PD] video analysis

[Mathieu Bouchard]

On Tue, 18 Mar 2003, Thomas Grill wrote:

> The project will be a long-term video installation of an analyzed video
> camera image which controls sound synthesis.

we've done that one...

> - which linux/PD/GEM etc. components would i need for video in and analysis?
> - any experiences concerning long-term (several months) video and audio
> stuff with PD under linux?

i haven't done it with jMax instead of PD, but I think the experience is
still relevant...

in Générique (http://www.pfoac.com/intro/artistes/ACe.html) we used
GridFlow 0.4.0 in jMax 2.5.1. the only issue we've had is slight memory
leaks... something like 16 or 32 bytes per frame... the system would crash
after a week or so. I fixed those and then it ran continuously for two
weeks (the rest of the show) and it could have run for much longer
according to our extrapolations.

while it's important to run stable software, you cannot escape physical
realities, eg. power outage. it's good practice to make it easy to restart
the computer and the programs (we failed to do that on that occasion and
we learned the hard way!).

> - which (cheap!) video-in device should be used?

USB cameras are low-bandwidth and so can't accomodate big resolutions.
Even if you get 240*320, then if it is YUV-4:2:0, then 2 out of 3 YUV
color channels are encoded at 120*160 (!!!)

We like analog cameras. Find the right shop for buying those (probably not
"consumer electronics" shops). Then use a capture card such as a PCI
BTTV. You can get 480*640 @ 30 fps and such.

________________________________________________________________
Mathieu Bouchard                       http://artengine.ca/matju