[mythtv-users] VBI subtitles with ivtv cards?

[Mark Cooke]

On Fri, 2005-09-23 at 10:19 -0400, Jesse Guardiani wrote:
> Joseph A. Caputo wrote:
> > On Thursday 22 September 2005 16:37, Isaac Richards wrote:
> >   
> >> On Thursday 22 September 2005 04:29 pm, Joseph A. Caputo wrote:
> >
> > So does that mean that they'll get embedded in the MPEG file, but Myth 
> > just can't parse them out yet?
> >
> > - Are they muxed into the MPEG in a standard way (i.e., could I view 
> > them with another program (mplayer, xine, etc)? )
> 
> AFAIK. In fact, projectx doesn't seem to have any problem demuxing the 
> mpegs either.
> I've burned several VBI laden mpegs to DVD using mythburn without any 
> problems.

The subtitles (and other VBI data) are muxed in using a private stream,
in an IVTV specific format by the IVTV driver (in ivtv-vbi.c).

The ivtv muxer breaks program-stream assumptions made in transcode about
the size of each stream unit being exactly 2048 bytes long.  Word was
that the 2048 byte unit size is specified in the MPEG spec, but I
haven't had time to plough through the docs yet.  I just wrote a
subtitle-stripper that I used before transcoding for storage.

Search the transcode archives for my august investigation in more
detail.  Word was that it might be happier demuxing transport streams
(but I have audio-sync issues in MythTV with TS and didn't have time to
investigate).  Another option would be to patch the ivtv encoder to pad
out and to use 2K block sizes if a program stream is being used.


Hans did state a long term goal of providing standards-based VBI data in
the IVTV stream on the IVTV list (or maybe the V4l list) not too long
ago.


There is a patch to MythTV that knows how to process the current IVTV
format - and it worked fairly well when I was playing with it in August.

http://mitglied.lycos.de/beebof/myth.html mentioned in Ticket URL:
<http://cvs.mythtv.org/trac/ticket/368> seems to be very similar to the
code I experimented with (Martin Barnasconi's work) and gave subtitle
display without needing to use a PVR350's output.


It will be great when this all works - as the embedded VBI data can
contain the WSS and automatic 4:3 / 16:9 switching could be done.


Have fun!

Mark