29-01-2024, 10:56 AM
The Whole concept of Additional services Like Ceefax/Oracle/Teletext Ltd and Datacast etc
and Anciliary services like Subtitles PDC and "this channel Programme listings" and related material (Synopses Recepies etc) (Plus AD etc)
was very powerful division of what was going on in the VBI.
(and subdivisions on the text services News, Sport , fuller Listings , informational , Advertsing etc)
In Simple terms
Anciliary services could be put on line pairs close to the Active Picture
and thus could be passed through the playout and distribution system with the picture.
the BBC passed through Line 20/333 Subtitles 21/334 One line ITS, 22/335 Notionally empty
Commercial PSB used 335 for subtitles and had 22 and I think 21/334 for the "mag6" Anc Text.
With Teletext LTd inserting at the Transmitters the itv companies only had Limited teletext kit may be just subtitles....
so When Teletext Ltd stopped transmitting those Itv companies without Ancilliary Text
lost all their subtitles being received ... (And thus were in breach which did not impress OFCOM)
as ALL TV sets cannot decode Intermittent Teletext (and thus are non complient with EN 300 706)......
Much panic with the engineers having to get something done (But Teletext Ltd did help)
and the Lawyers on how something that was being transmitted could not be recieved
- so the Station output extend beyond when the signal left the Building and relied on others with whom itv/Ch4 had no relationship (They also got a quick lesson on DVB SI)
..... much assistance from BBC - who had seen this one coming!
and Anciliary services like Subtitles PDC and "this channel Programme listings" and related material (Synopses Recepies etc) (Plus AD etc)
was very powerful division of what was going on in the VBI.
(and subdivisions on the text services News, Sport , fuller Listings , informational , Advertsing etc)
In Simple terms
Anciliary services could be put on line pairs close to the Active Picture
and thus could be passed through the playout and distribution system with the picture.
the BBC passed through Line 20/333 Subtitles 21/334 One line ITS, 22/335 Notionally empty
Commercial PSB used 335 for subtitles and had 22 and I think 21/334 for the "mag6" Anc Text.
With Teletext LTd inserting at the Transmitters the itv companies only had Limited teletext kit may be just subtitles....
so When Teletext Ltd stopped transmitting those Itv companies without Ancilliary Text
lost all their subtitles being received ... (And thus were in breach which did not impress OFCOM)
as ALL TV sets cannot decode Intermittent Teletext (and thus are non complient with EN 300 706)......
Much panic with the engineers having to get something done (But Teletext Ltd did help)
and the Lawyers on how something that was being transmitted could not be recieved
- so the Station output extend beyond when the signal left the Building and relied on others with whom itv/Ch4 had no relationship (They also got a quick lesson on DVB SI)
..... much assistance from BBC - who had seen this one coming!