Re: ISDB caption support

[Mauro Carvalho Chehab <mchehab@osg.samsung.com>]

Em Fri, 28 Nov 2014 22:23:13 -0500
Devin Heitmueller <dheitmueller@kernellabs.com> escreveu:

> > I realize captions is an application-layer function, and intend to work with
> > the CCExtractor team. Do any other applications already have ISDB caption
> > support?

I never actually checked how CC works on ISDB-T. On the MPEG-TS
tables I worked so far, ISDB-T is very close to DVB, so I would
expect that CC would also be close to the DVB descriptors for it,
but, as I said, I never actually read that part of the ARIB/ABNT
specs.

> Based on a Google search, it looks like dvbviewer can decode them:
> 
> http://www.dvbviewer.tv/forum/topic/41933-brazilian-terrestrial-isdb-tb-subtitles-closed-caption/
> http://www.dvbviewer.com/en/index.php
> 
> It's not open source, and it's not Linux, but at least it may give you
> something to compare against if you want to build the functionality
> yourself.
> 
> > For DVB and ATSC there's quite a bit of code written by several people for
> > teletext and captions -- has anything at all been done for ISDB captions?
> 
> Not to my knowledge.  I've done a ton of work with CC decoding in VLC,
> but haven't poked around at the other formats.
> 
> > It's used in nearly all of Central and South America, plus the Philippines
> > and of course Japan -- you would have thought someone has started on the
> > task?
> 
> From what I understand, most terrestrial TV in Japan is encrypted, so
> you're likely to not find many open source solutions which targeted at
> that market.  Presumably there is less of that in Brazil (why else
> would Mauro be doing all that ISDB-T work if there was no way to watch
> the actual video?).
> 
> > We're looking for a good solution for capturing television in Brazil, when
> > the signal is encrypted -- are there set-top boxes or tv capture cards that
> > handle the decryption so that the decoded signal is passed on with the
> > ISDB-Tb caption stream intact?

I'm not aware of any device that handles encryption in Brazil. Cryptography
is used only in Japan standard, as far as I know.

All channels here are in clear, at least for video/audio streams, but,
as I said, I never tried to work with CC for ISDB-T. Yet, I would find really
weird if just CC is encrypted.

> 
> This would be very unusual.  Satellite captioning often has the same
> issues - the decoders only support overlaying the captions over the
> video and provide no means to access the underlying data.
> 
> Devin
>