My digital TV sets can process signals from different input sources.
Ariel - Analogue TV signals (ATV)
Ariel - Digital TV signals (DTV)
Scart - AV1
Scart - AV2
One of my sets can work out (some of the time) that I am sending it a signal from a CD player and it switches accordingly.
Other sets need to be told which signal I wish it to process and display - there's a button on the set - it has an icon of a circle pierced by an arrow - I use this button to select the input required.
Peccavi, February 2011