Vertical Blanking Interval (VBI) Measurements
- Updated2023-08-17
- 2 minute(s) read
Vertical Blanking Interval (VBI) Measurements
Closed Captioning (CC)
Pattern(s): CC Data Line
Definition: This is a measurement of the “Closed Captioning” (CC) data in a single vertical blanking line of the specified frame (no averaging over multiple lines of frames). It is located on line 21 in each field of 525-line systems (it does not apply to 625-line systems). If the clock run-in and start bits are valid, then all subsequent data bits will be measured and decoded. Each CC line contains a clock run-in, two start bits, and two 8-bit characters, each comprised of 7 data bits and 1 odd parity bit.
| Measurement | Definition |
|---|---|
| Run-In & Start Pattern | Validation of the clock run-in and start bits as a binary pattern |
| Clock Start Time | Start time of the leading edge of the clock run-in measured at its 50% level |
| Clock Duration | Duration of the clock run-in measured at its 50% levels |
| Start Bit Gap | Duration of the gap between the end of the clock run-in and the leading edge of the third start bit |
| Clock Levels | High and low levels of the clock run-in |
| Data Rise and Fall Times | Rise and fall times of data bits measured between their 10% and 90% levels |
| Data Levels | High and low levels of the data bits |
| Character 1 | The 7-bit decimal value of character 1 and the value and type of its parity bit |
| Character 2 | The 7-bit decimal value of character 2 and the value and type of its parity bit |
Wide Screen Signalling (WSS)
Pattern(s): WSS Data Line
Definition: This is a measurement of the “Wide Screen Signalling” (WSS) data in a single vertical blanking line of the specified frame (no averaging over multiple lines of frames). If the run-in clock and start bits are valid, then all subsequent data bits will be measured and decoded. Each WSS line contains a clock run-in, start code, and data bits that define picture aspect ratio, height, and position. PAL data also contains other information. NTSC WSS contains a CRC code.
| Measurement | Definition | |
|---|---|---|
| Run-In & Start Pattern | Validation of the clock run-in and start bits as a binary pattern | |
| Data CRC | Verification of the data CRC | |
| Start Time | Start time of the leading edge of the clock run-in measured at its 50% level | |
| Data Rise and Fall Times | Rise and fall times of data bits measured between their 10% and 90% levels | |
| Data Width | Width of data bits measured between their 50% levels | |
| Levels | High and low levels of the data bits | |
| Aspect Ratio | Decoded aspect ratio from first data group (4:3, 14:9, or 16:9) | |
| Size | Decoded height from the first data group | |
| Position | Decoded position from the first data group (525 only) | |
525-Line Systems:
|
Decimal values of the 3 data words and the CRC (525 only) | |
625-Line Systems:
|
Decimal values of the 4 data groups (625 only) |