[MEncoder-users] ATSC closed captioning

[Reimar Döffinger]

On Mon, Nov 08, 2010 at 10:56:37AM -0800, Scott W. Larson wrote:
> >And btw. the second channel is in the second field, which both your
> >and SVN code discard.
> 
> In ATSC, captions are in the picture user data, not in the video. The EIA-608 data is tagged as either channel one or two. Yes there's no way to select which channel to display. So far I have not found any captions in the second channel of any ATSC broadcasts (only XDS data) so this wasn't a problem for me. This situation could change of course. Once Mexico starts converting to ATSC we can expect them to include both English and Spanish closed captions. It's likely that the English ones will only be available in the CEA-708 subtitles.

We have a sample: http://samples.mplayerhq.hu/sub/subcc/test1.mpg
However as far as I can tell it is quite idiotic in so far the two languages
are encoded on CC1+CC2, which share bandwidth and thus the spanish
subtitles are always delayed. The CC3+CC4 seem completely unused. Silly.
Anyway I think I managed to add support for selecting the channel,
-subcc now takes the channel number as argument.
Runtime selection as for other subtitles would of course be nicer.

> >However the biggest problem I have is the subcc_decode function in
> >SVN which claims to do EIA-708 but has not resemblance at all with it.
> >I suspect it might be CC-subs for DVDs and maybe they are different,
> >but it seems we do not have a single sample for that...
> 
> There is a passing reference in the comments to "the EIA-708 standard" but nothing that says it supports them.

I think it was meant as a reference to the encapsulation of EIA-608 data - however it seems to be a completely
different method from what CEA-708 describes...
And could someone please upload a sample? None of those we have here: http://samples.mplayerhq.hu/sub/subcc/
contains the string "GA94"...