If your set-top box is not correctly adjusted to the 4:3 format of your television screen, you will see a picture with anamorphic distortion, i.e., your television picture is vertically distorted.
A number of set-top boxes have the facility in their menu to adjust the format of the connected TV appliance using the remote control. Choose the menu item ‘letterbox format’. Please refer to the user’s manual for detailed menu navigation.
Unfortunately there is no standardization for menu terminology or navigation