4.9. Teletext Interface¶
This interface was aimed at devices receiving and demodulating Teletext data [ETS 300 706, ITU BT.653], evaluating the Teletext packages and storing formatted pages in cache memory. Such devices are usually implemented as microcontrollers with serial interface (I:sup:2C) and could be found on old TV cards, dedicated Teletext decoding cards and home-brew devices connected to the PC parallel port.
The Teletext API was designed by Martin Buck. It was defined in the
kernel header file
linux/videotext.h, the specification is available
(Videotext is the name of the German public television Teletext
Eventually the Teletext API was integrated into the V4L API with
character device file names
major number 81, minor numbers 192 to 223.
However, teletext decoders were quickly replaced by more generic VBI demodulators and those dedicated teletext decoders no longer exist. For many years the vtx devices were still around, even though nobody used them. So the decision was made to finally remove support for the Teletext API in kernel 2.6.37.
Modern devices all use the raw or Sliced VBI Data Interface VBI API.