We typically advise against using USB cameras with SecuritySpy. This is partly due to their general low video quality and short cable length, but also due to bandwidth limitations on the USB bus making it difficult to use multiple USB cameras at the same time. However, we understand that they can be an attractive option in some situations due to their low cost and simple plug-and-play connection to the computer. Therefore, a USB camera can potentially be a cheap and useful addition to a video surveillance system in certain circumstances.
One USB camera will use most of the bandwidth on a USB bus (this is because USB cameras use uncompressed video, as opposed to network cameras, which use compressed video). Therefore, it is not possible to use more than one camera on the same USB bus at full resolution.
Although Mac computers typically have more than one built-in USB port, they vary in how many USB busses they have. In some Macs, all the ports share the same bus, and therefore the same bandwidth. On other Macs there may be multiple busses. To see how many busses your Mac has, open the “System Information” app (“System Profiler” on systems before OS X 10.7) from your /Application/Utilities/ folder. Click the “System Report” button, and locate the USB section on the left side of the window:
The above system report is for a late-2009 Mac Mini. This computer has five USB ports, and as you can see, it actually has four separate USB busses. The first bus powers the built-in IR Receiver and USB port number 2; the second bus powers the built-in bluetooth controller; the third bus powers USB ports number 3 and 4; and the fourth bus powers USB ports 1 and 5. Note that there is no way to tell from the above information which busses power which ports! You either have to find out this information online or through trial and error. Note also that only the second two busses are “High-Speed”, i.e. USB 2.0. The first two are USB 1.1 busses, which are much slower (useful for bluetooth, keyboards, mice and other low-bandwidth devices only).
So, with the above computer, if you wanted to use two USB cameras, you would plug one into port 1 or 5, and the other into port 3 or 4, so that they are on separate high-speed busses. If you were to connect a camera to port 2, it would work poorly, or maybe not at all, because this port is on a USB 1.1 bus.
Similarly, if you use an external USB hard drive, this should be on its own high-speed bus for optimum performance. Therefore, in the above example, we have one camera using one high-speed bus, and one USB hard drive using the other high-speed bus.
If your computer has PCI slots (a Mac Pro for example), you can add extra USB ports using PCI cards. Note however that such cards typically have only one bus, and share this bus between all their ports, so it is likely that you will need one PCI card per USB camera.
Our advice remains: use network cameras, which don’t suffer the same limitations, and are designed for the purpose of video surveillance with typically far superior video quality. SecuritySpy supports a wide variety.