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[SOLVED] problem with streaming from two webcams with v4l2


I wrote a couple of days ago about a problem with streaming from two
webcams. I had errors when I tried to start both streams simultaneously
but individually they both worked fine.

According to a page on the matter (not sure if I'm allowed to post links
so I'll just quote):

"A USB camera uses all the bandwidth a USB1.1 controller can give. Even
at low framerates the camera reserves more than half the 11 Mb/s. This
means that the 2nd camera gets rejected. Few motherboards have more than
one controller. Often 2 or 4 physical connections on a motherboard
shares one and the same USB controller. To add more cameras you need to
put USB adapter cards. One per camera. There exists cards with full
bandwidth per USB socket. These present themselves as for example 4 USB
controllers to Linux and they work fine with 4 cameras. Also, many (if
not most) cheap PCI USB1/2 cards ($10 range) have a controller capable
of supporting 2 x USB1 cameras and an additional USB2 camera per card.
With those cards and USB1 extender cards (allowing extension of a USB1
device for up to 100m, typically 50m) you can have a capable
surveillance setup using only USB cameras.".

So the problem was fixed by adding a PCI card that had some extra USB
ports. Hope this helps others that have a similar problem.

Mircea Uifalean

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