Hello Mauro. Thank you for your quick reply. On Raspberry model B (1 core 700MHz) I can only watch 2 cameras with the resolution of 320x240 pixels. When I try to watch a single camera with full resolution, Raspberry hangs. That's why I tried to run Raspbian on my laptop - just to check, if a stronger machine (Raspberry pi 3 for example) would be able to play it. On laptop I can watch a single camera at full resolution. I didn't try if I can watch more of them at once at full reslution, but you are right, at full resolution a single camera would consume almost all usb 2.0 bandwidth, and I didn't think about it beforehand. Just happy with result, I installed zoneminder on the laptop machine. Zoneminder allowed me to watch all three cameras, but only at 320x240 px. And on one of them the picture was defective, as I wrote on my earlier e-mail. Then I started more tests and it turned out, that when I have connected 3 grabbers, I can't see the correct picture always from this single grabber, even if I watch only this one at 320x240px. 320x240px needs less than one fourth bandwidth of the full resolution picture bandwidth, so I think, it should work if I play a single camera at once. But it looks like I'm wrong. Nevertheless, it looks like that if I want to grab video from all of them at full resolution, I would need a single Raspberry Pi 3 per camera, but I must test it. Thanks, Tomasz wt., 14 maj 2019 o 14:05 Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx> napisał(a): > > The problem is related to the maximum bandwidth that an USB 2.0 > provides. Most audio and video devices like cameras use an type of > USB package, called ISOC, with allows reserving bandwidth for them. > It actually reserves a number of USB slots. The maximum is 980 slots > per second, if I'm not mistaken. > > The actual number of allocated slots depends on the resolution, > format, package size, number of frames per second, etc. > > I don't have the numbers for cx231xx, but, with em28xx, a 640x480, > 16 bits per pixel, 30 frames per second video uses about 60% of > the available USB 2.0 bandwidth. So, even two cameras at full > res can be too much. > > I guess you can consider your self lucky to be able of having > two cameras working :-) > > If you need more than that, you'll need to use a machine with > multiple USB buses and connect each camera on a different > bus. > > Thanks, > Mauro
