ANY-maze Help > Cameras and Videos > What's happening when ANY-maze reports that USB bandwidth has been exceeded

What's happening when ANY-maze reports that USB bandwidth has been exceeded

Introduction

If you connect multiple USB cameras to your computer, you may encounter a problem where the images from one of more of the cameras isn't displayed and in its place is a message saying The available USB bandwidth has been exceeded.

What this means is that the data being sent from all the cameras is more than the USB system can cope with, and therefore one or more cameras have been switched off.

What is the USB bandwidth?

The USB bandwidth is simply a measure of how much information can be sent through the USB cable in a unit of time and, as you'd expect, it’s finite. For most devices this doesn't matter, either because they send such a small amount of information that it uses hardly any of the bandwidth, or because the data isn't time dependent. Cameras, however, do send a lot of data and it is time dependent, and therein lies the problem.

In fact, the USB bandwidth limitation isn't a characteristic of the USB cable, it’s a characteristic of the USB controller and, just to make matters more complicated, a single USB controller typically connects to multiple USB ports. This means that you can easily connect multiple cameras to a single controller and, as each camera uses quite a lot of bandwidth, it's not hard to connect so many that all the bandwidth is used - this often happens when more than three cameras are connected to a controller, although there is no hard rule.

What can you do?

There are two things you can do to resolve this problem:

Connecting fewer cameras to the controller

If your computer contains multiple USB controllers, then you can unplug a camera from one controller and connect it to another one. For example, if you have four cameras all connected to the same controller then they may not all work. But if you have a second controller in your computer and you connect two cameras to each controller, then they probably will all work.

Of course this raises some questions: How do you know how many controllers your computer contains? And how do you know which controller your cameras are connected to? Answers to these questions, and indeed a detailed description of this whole issue, can be found in this guide on the ANY-maze website Connecting multiple USB cameras to a computer

Reducing the bandwidth each camera is using

If you reduce the bandwidth each camera uses then you will be able to connect more of them to the same controller.

There are two ways to reduce the bandwidth of a camera: reduce the size of the video image, and/or reduce the number of images the camera sends each second.

Usually reducing the number of images sent per second (called the camera's Frame rate) is the best option as most cameras send 30 frames-per-second (fps) but ANY-maze tracks fine when provided with just 15fps or even 10fps - after all in most behavioural tests the animals don't usually move very far in one tenth of a second.

You can reduce both the frame size (the size of the video pictures) and the frame rate as part of a video sources properties - full details can be found here. The guide I mentioned earlier, Connecting multiple USB cameras to a computer, also describes this in some detail.

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ANY-maze help topic T1336