[linux-dvb] Re: Closed Captioning

[Johannes Stezenbach <js@linuxtv.org>]

Dave Chapman wrote:
> Not sure if this is on-topic for this list or not, but here goes.
> 
> I live in Europe (hence the ignorance about closed captioning), but 
> there is a NTSC DVB feed available on Eutelsat W2 (16 degrees east) 
> which carries "The Late Show With David Letterman" at 4.30am GMT 
> (11.30pm ET) every morning.  I think this is how all the European TV 
> stations that broadcast the Letterman show get their copies.
> 
> This broadcast has flashing white dots at the very top of the picture, 
> and I am guessing that these are closed captions.    Is that correct, or 
> could they be another kind of data?

CC is in some VBI lines, i.e. outside the visible are and thus
not part of the MPEG encoded picture. There's an ETSI spec for
DVB CC which is similar to DVB teletext.

The flashing dots in the first line are most likely a timecode,
something like VITC but in the visible area so it doesn't get
lost during MPEG encoding.
It's also sometimes present in other broadcasts e.g. on Astra 19.2E.

Johannes