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Closed Caption in Digital TV - How?

Posted: Mon Nov 06, 2017 12:52 am
by spellkaw
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.

Re: Closed Caption in Digital TV - How?

Posted: Mon Nov 06, 2017 7:06 am
by w9wi
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.

Re: Closed Caption in Digital TV - How?

Posted: Tue Nov 07, 2017 3:43 am
by spellkaw
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.

Re: Closed Caption in Digital TV - How?

Posted: Tue Nov 07, 2017 4:45 am
by w9wi
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.