On 9 Oct 2001 at 9:16, Rich Drewes wrote: > Philipp Ineichen wrote: > > >Hi Peter > > > >In the meantime I changed the alternate setting from 3 to 1 in the > >cpia_usb_open function. Now, both cameras are able to set the alternate > >setting (interface = 1), but xawtv (gqcam as well) is still not able to > >display both streams! > >I think that there is enough USB bandwidth since I changed the alternate > >setting to 1. Am I right? That means that video4linux has troubles handling > >both cameras simultaneously? > > > As I indicated in an earlier post, there is a fairly simple userland solution to this problem: using semaphores to enforce exclusive access to the read system calls as I have done in my modification to the 'motion' V4L program (http://interstice.com/drewes/motion-2.6.2- with-semaphore.tgz). This doesn't reduce the total capture speed for all cameras though of course each camera captures at about half the speed it did individually. I have used this method to keep two USB cameras working simultaneously in a > security application for weeks at a stretch without any problems. > > I agree that a system level solution would be desirable, so if anyone > knows how to make that work, by all means, please advise. In the > meantime, my advice: use semaphores. Are you running two instances of motion? I'm attempting to do the same with a bttv card with 4 inputs, and up to 4 copies of motion.. I've hacked-up the example invert.c program (that came with vloopback, from the motion page) to go through each input, grab a frame, and output that frame to a loopback, like so: /dev/video i0 -> /dev/video1 /dev/video i1 -> /dev/video3 /dev/video i2 -> /dev/video5 /dev/video i3 -> /dev/video7 At this point, I'm only using 2 inputs, and the frame rate isn't too bad, but I think if it were to read a frame from each input, into it's own seperate bufffer, and have a seperate thread writing those buffers each loopback, it would be a little quicker. Now I'm not a programmer, I have no clue how to implement this. If you're interested, I've placed my (ugly) code at www.havokmon.com/stuff/multiout.c Rick -- Rick Romero IT Manager Valeo, Inc. ph 262.695-4841 fax 262-695-4850 rick@xxxxxxxxxxxx
