Apple Video System - Manual (Page 61)

The screen controls appear.
3 Click the video source you want to use.
Choose Video if your device is attached to the composite
video input port on the video input card, or S-Video if your
device is attached to the S-video input port on the video
input card.
You can also choose TV to view TV in the video window, if
you have a TV tuner card in your computer. To learn about
viewing TV on your computer, see the manual that comes
with the TV tuner card.
Note: If you’re not sure whether or not a TV tuner card is
already installed in your computer, check the illustration in
Chapter 4, “Troubleshooting.”
The source change takes effect as soon as you make it.
55 Learning About the Software