If you watch a high definition (HD) program (16:9 ratio) on a standard TV (4:3 ratio), it will place black bars at the top and bottom of the screen where there's no picture. Sometimes an HD channel will show a standard definition program with black bars on the sides, so if you're watching on a standard TV, you'll see black bars all the way around. If this happens, switch to standard broadcast for that network.
If you watch a standard definition channel on your HD TV, it'll place black bars at the sides of the screen where there's no picture. Sometimes a standard channel may show a widescreen program with black bars at the top and bottom, so if you're watching on your HD TV, you'll have black bars all around your screen. Some HD TVs have a zoom function for these programs so they can be set to fill the screen without distortion.
comment peut-on faire les barres noires en haut et en bas de l'écran sur mon téléviseur