----- "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... Best regards -- Bruno Viaris _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
