This is an area unused by the actual television - it has been left to give the television's electron beam time to return to the top of the screen, these days it is more historical than anything else. The electron bean scans your television screen from left to right, then flies back to scan the next line.It actually scans every other line, doing this some 300 times for each 'field'.
Supported Teletext providers include BBC Ceefax (BBC1 and BBC2) and RTE Aertel. Browse to a page by entering its page number in the text box.
Browse to the next or previous page with a press of a button or just sweep the finger over the screen.
Those coloured dots are the teletext signal, and look something like this: (this example is slightly blurry as it is from a video recording, and most videos do not preserve enough of the VBI to make it possible to 'record' teletext) HDTV is new, and different, and offers two resolutions (720p or 1080i) which have little in common with the older broadcast formats described here.
If you are interested in the actual format of the television frame, or about how teletext actually works, or even "what's that black hammer-shaped thing at the top of the VBI for? Simply visit your local library (or on-line bookshop, if you prefer) and look for books with interesting names such as "Television Receiver Servicing". I cannot remember the exact figures, but you get fifty 'fields' (25 frames) each second (60/30 for NTSC) and it takes a couple of frames to make a complete teletext page - thus meaning your data rate is about 12 to 20 pages per second, though I am open to correction on this number.
RTÉ Publishing, a division of Ireland’s national broadcaster, RTÉ, uses Sys Media’s PLASMA teletext production and management system to power the Aertel teletext services on both RTÉ 1 and RTÉ 2 as well as the internet.
To give bookmakers instant access to update their content on these Aertel services, RTÉ selected Sys Media’s Win SPRITE page editing technology.
On the other hand, though, teletext is completely free.
You don't pay any extra (over your normal licence fee) to receive it, and you don't need to connect to any sort of service to request pages.
Sys Media has provided RTÉ with an innovative IP-based teletext page editing system that allows bookmakers across the country to provide rapid updates to vital onscreen betting information.
The system is now fully operational following earlier trials.
Also, some things, such as the main index page, are broadcast more frequently than other pages (so people just turning on teletext don't see a blank screen for ages).