Teletext
Teletext Subtitling
Teletext subtitling, also known as closed subtitling, involves adding a stream of character codes representing the subtitle characters into the broadcast video signal. Suitably equipped TV sets or receivers can be set to decode the data and display the subtitles on screen. Historicaly this data is added into the VBI area of the video signal and this method is still used in analogue services. More recently the same data can be carried as a separate data stream in a DVB multiplex or as part of the VANC data in an HD digital video signal.
Details
Teletext subtitling is also known as a closed subtitling technique which means that viewers can choose whether or not to display the subtitles. However, do not confuse Teletext subtitling with the closed captioning system used in several countries including the U.S.A. For more on Closed Captions see Here .
Teletext can be used to transmit data in addition to subtitles including information pages, clocks and private data. The individual characters that make up a Teletext subtitle are represented by single codes which are then transmitted to the receiving equipment. The Teletext receiver then looks up the codes in an on-board table and displays the required characters on screen. Teletext is not suitable for all languages and the character sets installed in the receivers can also be specific to a country or region.
Character Sets and Languages
Latin - All West European and Scandinavian languages complete with all accents
Cyrillic - Russian, Ukrainian, Bulgarian etc.
Greek - Greek
Hebrew - Hebrew, Aramaic, Yiddish For a full list of Latin and Cyrillic languages see the language table Here
Delivery methods
VBI as part of a broadcast signal - See the Polistream T3000 inserter
VBI as part of a media file or on a media server - See MediaMate file based solution
DVB Teletext as part of a broadcast signal - See the Polistream system
DVB Teletext as part of a stream file - See MediaMate file based solution
VANC data in an HD broadcast signal - See the Polistream system
VANC data as part of an HD media file or on a media server - See MediaMate file based solution
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Teletext Output Styles:
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Click on image to enlarge to see how the final output would look at full resolution.
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Teletext
Examples of Teletext Character Sets. Click on the tables to see a larger version.
These are examples of how the Teletext character sets works and do not represent all the characters available.
 
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| VBI Based Subtitling Diagram | | | | | |  | | | | | | | | | | |
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