How did the TV know what closed captions to show when VHS tapes were played?


How did the TV know what closed captions to show when VHS tapes were played?

In: Technology

The TV doesn’t know anything. The captions were stored on the tape in a section that doesn’t appear on-screen, but could be interpreted by a closed caption decoder.

I didn’t even know this was a thing.

If you couldn’t turn them off I’d assume it was just a part of the video. If you could turn them off/on there would have to be an encoded signal that the vcr could understand and selectively put that “layer” over the program material.

Hopefully someone else can do better than me.

CC was stored in the Vertical blanking back in the analog days of TV. It’s In the crt scan lines that you can’t see unless with a broadcast monitor. Generally line 21. Active picture started on line 22 for NTSC SDTV.

Source: myself. This is my career, though no analog anymore, all digital.

Closed captions are very simple digital data encoded in line 21 of the video. Line 21 is not displayed on normal tvs. However if you have an old VCR and TV you can adjust the vertical hold until the picture rolls and then you can see the caption data appearing as lines and dashes in the black area above the picture as it rolls.

Tbh when I was a kid, I always thought that someone was furiously typing up the captions as I was watching the movie

A VHS tape was just a recording of the analog signal that would be sent over the air/cable to a TV. It can contain all the same information in that signal, including the metadata like closed caption.