Widescreen signaling

In television technology, widescreen signaling (WSS) is a digital stream embedded in the TV signal describing qualities of the broadcast, in particular the intended aspect ratio of the image. This can be used by a widescreen TV or other device to switch to the correct display mode.

PAL and SECAM Systems

For 625 scan line systems (PAL and SECAM), the signal is placed in line 23. It begins with a run-in code and start code followed by 14 bits of information.

Group 1 (Aspect Ratio)

b00	b01	b02	b03	Aspect ratio	Picture placement	Active lines
0	0	0	1	4:3	Full	576
1	0	0	0	14:9	Letterbox centre	504
0	1	0	0	14:9	Letterbox top	504
1	1	0	1	16:9	Letterbox centre	432
0	0	1	0	16:9	Letterbox top	432
1	0	1	1	>16:9	Letterbox deeper than 16:9	<432
0	1	1	1	14:9	Full-height 4:3, framed to be "14:9-safe"	576
1	1	1	0	16:9	Full-height 16:9 (anamorphic)	576

Group 2 (Enhanced Services)

b04	Mode
0	Camera Mode
1	Movie Mode

b05	Mode
0	PAL Standard
1	Colour Plus

b06	Mode
0	No Vertical helper
1	Vertical helper present

b07	Ghost cancellation

Group 3 (Subtitles)

b08	Mode
0	no subtitles
1	Teletext subtitles

b09	b10	Mode
0	0	No subtitles
1	0	Subtitles inside active image
0	1	Subtitles outside active image
1	1	Reserved

Group 4 (Other)

b11	Mode
0	No surround sound information
1	Surround sound mode

b12	Mode
0	No copyright asserted or status unknown
1	Copyright asserted

b13	Mode
0	Copying not restricted
1	Copying restricted

NTSC Systems

525 scan line systems (PAL-M and NTSC) put the WSS data in lines 20 and 283. A start code consisting of the bits "10" is used, followed by 14 bits of information.

Word 0

b0	Aspect Ratio
0	4:3
1	16:9

b1	Mode
0	Normal
1	Letterbox

b2-b5 all have the value "0".

Word 1

b6-b9 are reserved and all have the value "0".

Word 2

b10-b13 are reserved and all have the value "0".

See also

• PALPlus
• Active Format Description (AFD)

References

• ETSI EN 300 294 "Television Systems: 625-Line Television Wide Screen Signaling (WSS)"

External links

• PDF of WSS standard
• PDF of WSS in 625 lines and 525 lines standard