Where does this come from, and can I check it?

American captions were coded into line 21 of the vertical blanking interval. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

Is this really a movies & tv fact?

Yes. It sits on the Movies & TV shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.

What else can I read about it?

The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.

Mondo Knows Facts

Closed captions rode in an invisible line

American captions were coded into line 21 of the vertical blanking interval Line 21 sits in the black gap between frames where the picture cannot show it. A caption decoder read the encoded text and laid it over the screen, which is why captions could be switched on or off. The CEA-608 standard set how the characters were packed in. It sits in Mondo's movies & tv collection, one of 200 facts that each trace back to the reference below.

Where this comes from

Encyclopaedia Britannica

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

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Technology trivia

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Tags: captions, broadcast, accessibility

Closed captions rode in an invisible line: the short answers

Where does this come from, and can I check it?: American captions were coded into line 21 of the vertical blanking interval. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a movies & tv fact?: Yes. It sits on the Movies & TV shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.