At the first glance, this seems to be senseless, but it may help developers of QuickTime applications to find problems in conjunction with macam. Open the file "net.sourceforge.webcam-osx.common.plist" in the Preferences folder in your Library folder in your home folder (if you're a developer, you are probably already familiar with the PropertyListEditor application). In the main dictionary, add an entry with the key "Dummy cameras" (if it's not already there). The value should be a Number type. Enter the number of desired dummy cameras (0 for default behaviour without dummies). At the next launch, you see your entered amount of simulated camera devices. Each produces a color bar image with a timecode.
For best recording performance with other applications, make sure that the preview or recording window size matches exactly the size of the images sent from the camera. In this case, a rescaling step can be skipped which could otherwise reduce performance.