Widescreen signaling
In television technology, Wide Screen Signaling is digital metadata embedded in invisible part of the analog TV signal describing qualities of the broadcast, in particular the intended aspect ratio of the image. This allows television broadcasters to enable both 4:3 and 16:9 television sets to optimally present pictures transmitted in either format, by displaying them in full screen, letterbox, widescreen, pillar-box, zoomed letterbox, etc.
This development is related to introduction of widescreen TVs and broadcasts, with the PALplus system in the European Union, the Clear-Vision system in Japan, and the need to downscale HD broadcasts to SD in the US. The bandwidth of the WSS signal is low enough to be recorded on VHS. It is standardized on Rec. ITU-R BT.1119-2.
A modern digital equivalent would be the Active Format Description, a standard set of codes that can be sent in a MPEG video stream, with a similar set of aspect ratio possibilities.
625 line systems
For 625 line analog TV systems, the signal is placed in line 23. It begins with a run-in code and starts code followed by 14 bits of information, divided into four groups, as shown on the tables below :Note: The transmitted aspect ratio is 4:3. Within this area a 14:9 window is protected, containing all the relevant picture content to allow a wide-screen display on a 16:9 television set.
| Bit | Item | Group |
| 4 | Camera Mode / PALplus Film Mode | 2 - Enhanced Services |
| 5 | Conventional PAL / PALplus Motion Adaptative Colour Plus encoding | 2 - Enhanced Services |
| 6 | No Vertical helper / PALplus Vertical helper present | 2 - Enhanced Services |
| 7 | Reserved / Ghost cancellation | 2 - Enhanced Services |
| 8 | No subtitles / subtitles within teletext | 3 - Subtitles |
| 9 | No open subtitles / Subtitles in active image area | 3 - Subtitles |
| 10 | Subtitles out of active image area / Reserved | 3 - Subtitles |
| 11 | No surround sound / Surround sound mode | 4 - Reserved |
| 12 | No copyright asserted or status unknown / Copyright asserted | 4 - Reserved |
| 13 | Copying not restricted / Copying restricted | 4 - Reserved |
525 line systems
525 line analog systems made a provision for the use of pulses for signaling widescreen and other parameters, introduced with the development of Clear-Vision, a NTSC-compatible Japanese system allowing widescreen broadcasts. On these systems the signals are present in lines 22 and 285, as 27 data bits, as defined by IEC 61880.The following table shows the information present on the signal, based on Rec. ITU-R BT.1119-2 :
| Bit | Item |
| 1 | Reference signal |
| 2 | Reference signal |
| 3 | Aspect ratio |
| 4 | Even parity for B3 to B5 |
| 5 | Reserved |
| 6 | Field type |
| 7 | Frame type |
| 8 | Vertical temporal helper |
| 9 | Vertical high resolution helper |
| 10 | Horizontal helper |
| 11 | Horizontal helper pre-combing |
| 12 to 14 | For TV station use |
| 15 to 17 | Reserved |
| 18 to 23 | Error correction codes for B3 to B17 |
| 24 | Reference signal |
| 25 to 27 | Confirmation signal |