h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is not a feature of North American/Japanese (NTSC) television.

The September 1976 BBC paper gave a brief sketch of how the PAL teletext system could be adapted for NTSC.

It's definitely been tried in the USA sometime in the 1980s, but obviously never caught on.

jd

Hm, definitely never caught on, or perhaps was called something different. Had it been tried in a major way there would have been much made of new sets which were capable of receiving the stuff, but that never happened to my knowledge (and I was old enough in the 80s to be aware of such a thing ).

Sets do come with built-in closed-captioning ability these days (used to need an add-on box for that until about 10-15 years ago), but I'm gathering that works slightly differently and is not related, as the idea there is to have text on the screen at the same time as the picture in order for the hearing impaired folks to be able to know what is said. When I was growing up, it was a big deal for things to be cc, but now it's pretty normal except maybe for certain live programs.

The one extra feature that's little-used is SAP. This came about when stereo sound broadcasting first appeared. It allows for broadcasting a second audio track to the same picture, such as to offer sound in a different language. I think all stereo-capable sets have SAP as well, but very few things make use of it.

Right on all counts, I think.

The experiments I read about were small trials in isolated areas. I don't think that any NTSC-teletext TVs were ever sold commercially.

CC does, as you say, use a completely different system. I mean it's superficially similar, but it's not like a derivative of teletext.

Teletext does support CC (or subtitles as it's known here). In the UK, they're always on page 888 (by convention). There are special characters in the character set that specify where the text boxes start and stop. Then the text is overlaid on top of the image. I think most programs are subtitled here, including many live news programs; for those, they have people typing on those stenotype keyboards (I think I've got the name right), and it can be amusing when the subtitle is phonetically correct, but spelt appallingly, or even made up of completely the wrong words! e.g. "Isolated" appears as "Ice elated"!