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Teletext on analog tv was additionally gradual. At the very least. The expertise was gradual.
Teletext labored on the precept of transmitting knowledge with out management of the receiver (identical to watching TV or listening to the radio within the first place). All of the pages have been broadcast one after the other (that quantity you see passing by). Your tv waits for the quantity you requested to come back up and ‘remembers’ that web page for you and thus confirmed it. He ‘ignored’ the opposite pages for you.
Nonetheless, extra fashionable CRT televisions (but additionally the ‘flat TVs’) had change into smarter for the teletext expertise. They listened and remembered ‘all pages’ (you noticed that they may bear in mind 999 pages with the specs) that got here by and once you began teletext you really labored from a sort of cache in your TV for the channel you second seemed.
in different phrases. Should you had simply gone to the channel, not all pages have been cached but, so it might initially take ‘a very long time’ earlier than you noticed the primary web page, however as soon as he had achieved a spherical of all pages you might simply browse them . Some pages had ‘subpages’ (ie if a information article consisted of multiple picture, or TV guides, and so on.) and they also all needed to undergo one after the other, in order that you might browse all of them too.
In follow it typically occurred that not all pages have been cached by these subpages (which might add up fairly a bit should you might cache ‘solely’ 999 pages), however the TVs did have a sort of intelligent concept that they primarily cached the proper pages .
Good element (at the least, I feel it is humorous):
The information of the teletext info was bodily transmitted ‘above the image’. (so on picture line -20 to -10 or so. I identify it). There, ‘pulses/pixels’ are broadcast, which the TV tuner picked up and transformed into textual content/blocks/traces. Thus, every station might ship its personal teletext knowledge.
Edit: Disclaimer on the above. It’s worded considerably simplified. Truly, it was broadcast ‘between frames’ within the Vertical Blanking Interval, however going into that an excessive amount of requires extra data of CRT than I’ve.
In my view, with digital tv, as quickly as you request the channel, all teletext knowledge is distributed for that channel in a single go, so that you even have every part in a single go. The identical as watching teletext by way of the web on a pc or one thing. (in fact it is just a few thousand pages of textual content in the long run, so it in all probability will not be a lot multiple or two MB of knowledge (which might be despatched compressed too))
[Reactie gewijzigd door lenwar op 5 september 2022 13:41]
