[PD] advice- multiple camera inputs

Martin Schied crinimal at gmx.net
Sun Aug 8 16:31:36 CEST 2010

Dima Strakovsky wrote:
> Hi all, 
> Coming out of the lurker mode to ask a question here :) I am kicking around an idea for a work that would require four camera inputs. The video streams would be remixed in realtime and output via a single projector. Was wondering if anyone has played with the scenario and has some advice  to offer? 
> OS-wise I could go with ether OsX or LInux. I am looking for the max resolution from each input. Hopefully at least 320X240. Ideally higher. Camera-wise I was looking at two solutions 1. four cameras go into a multiplexer and then I grab the four different quadrants from the video stream or 2. four firewire cards (might be too much of a brute force solution:) + might run into some interesting driver issues).  Also, is there an advantage to having two boxes processing inputs and then sharing them over a network i.e. using more then one computer for this work?  
> Any advice would be very much appreciated. Thank you.

I built an installation together with an Artist last summer, using up to 
6 USB 2.0 web cams running at 640x480, 30fps each, using a single 
computer. We used "driverless" cameras (UVC standard) which worked out 
of the box on OSX (logitech  vision pro for mac), but you also could use 
any usb 2.0 camera with uncompressed output too. There are independent 
driver projects for some of them, so have a look.

I used GEM to mix / arrange all camera images together and pix_blob and 
some more pix_ objects for motion detection on osx. this took 50% cpu on 
a macbook pro on both cores ( a 2x2.2 GHz model).

Initially I also tried different debian distributions and the same usb 
cameras (worked out of the box too). When I tested them they all caused 
too high cpu usage, not only in pd/gem - approximately 50% to 60% on a 
single core @ 1.7GHz. This was approximately 1 year ago, so maybe there 
are some improvements now. Maybe I was unable to deactivate jpg 
compression or so - I never had time to find the exact reason for this - 
so if someone can tell more...

At least I could use one of these cameras in 'guvcview' later which only 
used 15% cpu of a 1.8GHz core.

So from my experience - if you are no experienced linux user, you'll be 
less annoyed using osx and many usb cams. I have no experience with many 
firewire cameras, I never had a chance to use more than one, and this 
was only a DV cam, causing latency and high cpu usage for decoding.

One annoying thing about USB cameras are the cable lengths which should 
be considered first (you can chain many usb hubs or repeater cables though).


More information about the Pd-list mailing list