Hi, 2010/5/16 <bruno.via...@free.fr>: > > ----- "Adrian Sergiu Darabant" <aser...@yahoo.co.uk> wrote : > >> My need is to stream from both cameras in the same time. > (...) >> I tried to do that and I am succeeding up to query and map buffers but >> then when doing VIDIOC_STREAMON - the first camera starts and the >> second one always gets >> >> kernel: uvcvideo: Failed to submit URB 0 (-28). >> >> which seems to be linked with the usb bandwidth. > > Hello Adrian, > This problem is mentioned in the "Motion" software FAQ: when streaming from > multiple USB cams, each one must be plugged to its own USB controller, not on > a hub, including motherboard hubs (typically the pair of connectors on top of > each other). > (cf http://www.lavrsen.dk/foswiki/bin/view/Motion/FrequentlyAskedQuestions > first item) > > I experienced this problem on an eeepc 701 / linux: while streaming only > v...@1fps the two webcams (Vesta pro + SPC900) had to be plugged one on each > side of the netbook. > But I could plug an external harddrive (recording both streams!) in the same > hub as one of the cams! Go figure that... > Same thing on a Dell desktop PC with Hercules cams under windows XP. > >> >> I don't know all the details about the USB transfer protocol but my >> understanding is that - the driver should request a static bandwidth >> allocation before starting streaming. Would it be possible to force >> the streaming at a lower rate - maybe loosing some frames from the >> camera but still allow multiple camera streaming ? > > Using distinct controllers is obviously just a workaround, but I have no idea > if this bandwidth allocation problem can be dealt with at the driver level, I > will leave this to competent people... >
I think the problem with some cameras is that they request more bandwidth than they actually need, so this causes this type of issue. I've add no problem in streaming 2 QuickCam cameras from the same controller in MJPG, but for other models/vendors it fails with the exactly same settings. Best Regards, Paulo > Best regards > > -- Bruno Viaris > _______________________________________________ > Linux-uvc-devel mailing list > Linux-uvc-devel@lists.berlios.de > https://lists.berlios.de/mailman/listinfo/linux-uvc-devel > _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
