On 27/08/10 15:14, Martin wrote: > The problem: > > From reading around this list and elsewhere, it appears that you simply > cannot run more than one webcam video stream per USB root hub. > > When enabled for video streaming, the webcam reserves the full > isochronous bandwidth needed to stream data at the selected resolution > and framerate, regardless...
Kindly, a direct reply suggested: #### ...the only way I've managed to get multiple cameras working was by using the mjpeg format. I've got this way working 3 cameras at 10fps 640x480 resolution on same root usb hub - and it looked like I might be able to get a fourth one. I would suggest you start by checking the specs for your cameras - if they are supposed to support mjpeg. Don't know how you are trying to get them working on mjpeg, but I used the command: ffmpeg -vcodec mjpeg -f video4linux2 -r 10 -s 640x480 -i /dev/video0 ouputfile.ext The '-vcodec mjpeg' has to go in front of the '-i' option in order to request the stream in mjpeg format from the camera - after the '-i' it will merely convert the stream to mjpeg. #### Tried that and a few variations... Although the mjpeg streaming is accepted, there is no output. I've had the same non-result with other applications I've tried for getting a mjpeg stream from the WV060 webcam and the uvcvideo driver. > *A possible solution* ? > > Instead, could the UVC driver 'simulate' a reduced framerate by instead > using the "STILL_IMAGE_FRAME" mode of the webcam and grab for itself a > set number of images per second? Or even only when polled by a read from > the user application? > > On *nix, "everything is a file"... Could the uvc driver accept reading > of /dev/videoX by the command "cp" so that still image data is copied, > formatted for a jpg or png? > > Could the "quirks" setting be abused to set the image grab rate? Or some > other neater method? That still looks to be the best solution. The webcam is supposed to support still image capture, but how do I do that?! Is there a nice little snippet of C code that I can compile to grab a still image to a jpg or png? A gruesome work-around that does work is to use old USB 1.1 hubs to force the WC060 to a lower data rate. You can then have many webcams connected to your system! However... The WC060 reduces the maximum resolution to 640x480 rather than reduce the framerate. Quite a waste for the 1600x1200 that it supports; The USB 1.1 hubs must be plugged directly into the USB 2.0 root hub for a USB 1.1 root hub to be allocated (or for the UVC driver to work?); Use "lsusb -t" and "lsusb -v" to see what is happening. The USB 1.1 hubs that I picked up for very cheap correctly announce themselves as USB 1.1 but have a product name of "USB hub 2.0". Very Marketing-esq nasty! eg: Bus 003 Device 002: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 9 Hub bDeviceSubClass 0 Unused bDeviceProtocol 0 Full speed (or root) hub bMaxPacketSize0 8 idVendor 0x05e3 Genesys Logic, Inc. idProduct 0x0606 USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub bcdDevice 7.02 iManufacturer 1 ALCOR iProduct 2 USB Hub 2.0 Note: "Full speed" = USB 1.1 and "High speed" = USB 2.0 ... Hence, despite the confusing "2.0" in the descriptors, it is actually USB 1.1. Is the UVC driver still being developed? Are there features support yet to be added? Or is all this a problem of the user-side application software? Regards, Martin > Further details: > > I'm trying to use two webcams simultaneously: > > iManufacturer 1 Sweex > iProduct 2 WC060 Series HD Webcam > > > On separate hubs, they work fine. On the same hub, the second one to > start shows the error: > > "Error starting stream VIDIOC_STREAMON: No space left on device". > > I've only got the one root hub on the system I want to use for the two > webcams! > > > Their descriptors show: > > bFrameIntervalType 2 > dwFrameInterval( 0) 2000000 > dwFrameInterval( 1) 4000000 > > > Can I tweak the UVC driver to preferentially choose the slower frame > rate available? > > Aside: The MJPG format doesn't seem to work, nor are any compression > settings visible... > > > Given a few hints or a patch, I can hack the kernel module to test :-) > > This is running on Gentoo, kernel 2.6.34 using the in-kernel uvc module. > > Any comment/ideas welcomed. > > Regards, > Martin > > > > > From lsusb -v (excerpt): > > VideoStreaming Interface Descriptor: > bLength 34 > bDescriptorType 36 > bDescriptorSubtype 5 (FRAME_UNCOMPRESSED) > bFrameIndex 9 > bmCapabilities 0x00 > Still image unsupported > wWidth 1600 > wHeight 1200 > dwMinBitRate 768000 > dwMaxBitRate 196608000 > dwMaxVideoFrameBufferSize 3840000 > dwDefaultFrameInterval 2000000 > bFrameIntervalType 2 > dwFrameInterval( 0) 2000000 > dwFrameInterval( 1) 4000000 > VideoStreaming Interface Descriptor: > bLength 42 > bDescriptorType 36 > bDescriptorSubtype 3 (STILL_IMAGE_FRAME) > bEndpointAddress 0 > bNumImageSizePatterns 9 > wWidth( 0) 640 > wHeight( 0) 480 > wWidth( 1) 352 > wHeight( 1) 288 > wWidth( 2) 320 > wHeight( 2) 240 > wWidth( 3) 176 > wHeight( 3) 144 > wWidth( 4) 160 > wHeight( 4) 120 > wWidth( 5) 800 > wHeight( 5) 600 > wWidth( 6) 1280 > wHeight( 6) 960 > wWidth( 7) 1280 > wHeight( 7) 1024 > wWidth( 8) 1600 > wHeight( 8) 1200 > bNumCompressionPatterns 9 _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
