Here I want to talk about VBI, the abbreviation of Vertical Blanking Interval. The television signal includes a part of the non-visual signal, which carries no visible information, and is therefore called VII (vertical blanking interval). VBI can be used to convey other information, usually a dedicated subtitle signal
Vertical Blanking Interval (VBI)
vertical retrace period
The TV images we usually watch are produced by the high-speed bombardment of the fluorescent substances on the picture tube by the electron strings emitted by the electron gun. The electron strings scan the entire screen from left to right and from top to bottom because the speed is very fast. So our eyes can't feel it. When the scanning position of the electron gun reaches the lower right corner from the upper left corner, it must return from the lower right corner to the upper left corner to start the next scan. The time it takes to return from the lower right corner to the upper left corner is the vertical retrace Period, this period of time is a waste for equipment, so people have found a way to use this period of time, TV stations can use this time to send some non-displayable information, if you have used teletext, you will immediately understand why The teletext card needs to receive TV signals. The TV card can interpret this information, but the TV cannot. This information is sent using the vertical retrace period. The TV card transmits the received non-displayable information to the computer through the RS-232 port , processed by the computer, this is the principle of teletext, that is to say, the TV station uses the vertical retrace period to send some non-displayable information, and the teletext card receives this information, and sends it to the computer after decoding computer processing.
This kind of information transmission is called VBI information transmission. An open international standard for this kind of information transmission is called North American Basic Teletext Specification (NABTS), which is used in Europe, South America and the Far East. Other standards include WST, Gemstar and Nielsen
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