[CentOS] Webcam Recommendation required

Mon Apr 3 18:17:27 UTC 2006
Lamar Owen <lowen at pari.edu>

On Thursday 30 March 2006 19:43, Sanjay Arora wrote:
> All these cams are 100$ plus whereas webcams for windoze are available
> for 10-20$.

Even the $10 cams work fair under Linux.  However, most USB cams use 
isochronous transfers (which eliminates SRAM framebuffering and glue logic on 
the cam, which is why they are so cheap); more than one device on the USB 
cannot go isochronous at one time (in practice this is true, although there 
are no software safeguards to prevent it).  You might get away with two USB 
isochronous cameras at once, but three is really asking for it (been there, 
done that.  Ruined a complete project because of it; needed four cameras plus 
a USB control interface on a single PC, and would not work, on Windows or 
Linux; saved a few dollars on the cams and wasted hundreds on getting it to 
work.  The PC was a full-bore Dell PowerEdge Xeon server with three UCB 2.0 
controllers; it simply did not matter, as when two isochronous devices needed 
servicing at the same time things broke, all the way up to hard kernel hangs.  
Now, these were in the days of Fedora Core 2, and prior to the release of 
CentOS 4, so perhaps things have changed; funding for that project has ended, 
and the project terminated.).

The network cameras present virtually zero load to the hosting PC.

> Whats the difference....something must b different in hw. Why should
> one buy these rather than the cheap ones? any performance/bandwidth
> optimization gains or maybe picture clarity?

The VCenter and Gadspot cameras are Ethernet cameras and full fledged 
microservers in their own right, and are a joy to use.  You use curl or 
similar to grab images, or gateway directly to the camera for streaming jpeg.  
No PC required for the streaming side; $100 each is cheap compared to a PC.

The cheaper the camera, the more is offloaded to the PC; and even the fastest 
PC made cannot do multiple isochronous devices without issue.
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772