Television is broadcast with different aspect ratios: 4:3 or 16:9 format. To allow the television to switch its display format, Wide Screen Signaling (WSS) transmits a special identification signal in line 23 in the vertical blanking interval
. When the TV receiver receives the WSS signal, it switches its display format from the standard 4:3 format to widescreen
16:9. In digital TV, the WSS information is inserted into the DVB data stream.
The WSS signal is also used to identify PALplus.