Closed Caption in Digital TV - How?

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spellkaw
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Closed Caption in Digital TV - How?

Post by spellkaw » Mon Nov 06, 2017 12:52 am

Hi,

there is a new law in our country to include closed caption in TV broadcast.
how do this closed caption works? is there a diagram or solution that we can follow?
or the strategy varies per TV operators?

Thanks.

w9wi
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Re: Closed Caption in Digital TV - How?

Post by w9wi » Mon Nov 06, 2017 7:06 am

What is the digital TV standard in your country?

In the USA the EIA-708 standard is used for captions. In practice captions are found in the ancillary data of the SDI video stream and encoded into the video stream in the MPEG-2 encoder.

I would start by checking the specifications for your MPEG encoders. I see captions are done a bit differently in DVB-T (apparently they constitute a separate elementary stream) but if I had to guess I'd say the MPEG encoders are still responsible for encoding them.
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Doug Smith W9WI
Pleasant View, TN EM66

spellkaw
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Re: Closed Caption in Digital TV - How?

Post by spellkaw » Tue Nov 07, 2017 3:43 am

Thanks Doug! actually we adopted the Japanese ISDB-T standard.
Our encoders support both 608 and 708 and the selection setting is kinda straightforward.
But where do we encode the closed caption text? is it on the editing machine like for example we are using adobe premiere?
or do we need to buy a separate machine for closed captioning?

Thank you.

w9wi
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Joined: Tue Feb 05, 2008 11:40 am
Location: Pleasant View, Tennessee
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Re: Closed Caption in Digital TV - How?

Post by w9wi » Tue Nov 07, 2017 4:45 am

Ah.

I don't know of any way to do it on the editing machine. You do need a separate caption encoder. I Googled on "ISDB-T caption encoder" and found this:
http://www.eitv.com.br/en/produtos/wohl ... ecoder-cc/

This one is for Brazil; I'm not certain it will be correct for other countries.
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Doug Smith W9WI
Pleasant View, TN EM66

Euclid
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Re: Closed Caption in Digital TV - How?

Post by Euclid » Thu Apr 18, 2019 10:35 pm

I am in Washington DC (USA). Here network programming usually has closed captions already inserted. Syndicated shows are the same. We setup everything to pass Closed Captions including sat receivers, up/down converters, recording equipment, and Master Control.

Local shows and a few shows produced for us do not have closed captions. We have several ways to add them.
1) We have Closed Caption encoders on the outputs of our production control rooms. We caption live shows and most local production there.
2) We have Closed Caption Encoders in the Air Path between the output of Master Control and the MPEG encoders. We add closed captions there to programs that do not have them. These encoders are also emergency backups for live shows.
3) For a few programs that arrive without captions we play the program through a control room and add captions.

Most of our edited pieces are short segments for insertion into live shows or production shows. The captions are added in the control room when the show is produced. i'm sure there are ways to add captions to pre-recorded material but we just don't do it here. You should ask your editing software supplier. It might be an option.

In the USA closed captions are not required on channels that have viewership below a certain number.

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