Hi Laurent, On Thu, 2007-05-10 at 10:56 +0200, Laurent Pinchart wrote: > Hi Julien, > > > I am working on video capture with several cameras. > > I have Logitech QuickCam UltraVision webcams. > > > > Is it possible to reduce the number of packets per isochronous URB in > > uvcvideo driver? > > By default, UVC_MAX_ISO_PACKETS is egual to 40. > > Yes that should be possible. I'm curious, why do you want to do that ?
I try to capture images with several synchronized cameras. I started with 2. In the configuration I use my cams, (2 captures at JPEG VGA 30fps), I observe: - An image output period granularity of 5ms for each camera (difference between 2 consecutive images queued in the same cam is either 30ms or 35ms). This comes from the fact that an URB is received in uvc driver every 5ms (40 packets of 125us). So as the real period of the streaming emitted by the camera is 30fps (I verified with packets PTS and SCR fields), an EOF is detected (and the corresponding image is queued) by uvc after 30ms, or 35 ms sometimes. - A image synchronisation jump between 2 cameras. When my 2 cameras are synchronized more or less, I still observe some delay jumps of 35ms immediately recovered on the next frame. My explication is: Let's suppose my 2 cameras are synchronized.The 5ms period granularity makes that potentially 1 image can be queued in one driver 5 ms after the corresponding synchro image on the other driver. During these 5ms, if I dequeue an image (VIDIOC_DQBUF) on the 2 driver, I put the 2 queues in a different state.=>one frame desynchro That why I would like to minimize this 5ms time.. > > > When I change this value to 10 for example, image capture with 1 cam > > works fine. However, as soon as i add and capture from a second camera, > > images on both cams appear wrong (bad colours, image cut).. > > Does it work with 40 packets ? Yes 2 cams capture works fine with 40 packets. For info, it works also for any higher multiple of 40 (80, 120, 160 ..packets), but not for any other value.. I can't explain why.. Thanks for reading and your help! Regards, Julien > > Cheers, > > Laurent Pinchart _______________________________________________ Linux-uvc-devel mailing list [email protected] https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
