[mythtv] Re: Teletext and /or subtitles in myth

[Martin Barnasconi]

Guess this fits better in mythtv-dev...
(Originally posted in mythtv-users)

> - There is an option inside the config screens of myth, that let you use
> subtitles in "PAL Teletext". Does anybody if this works for teletext
> subtitles, sent into page 888, and how to config it? As far as I know,
> this was only available for "closed Caption" subtitles, but not the ones
> in page 888 of teletext, but the name now seems something different.

Currently, subtitles are extracted from a /dev/vbi device (if available). The 
code is based on the alevt teletext decoding stuff and added to the nuppel 
player and recorder code. Page 888 is indeed the default page (somewhere 
defined in the mythconverg mysql database.)
For PVRxxx (ivtv) cards the vbi decoding is not yet implemented, as it uses a 
different recorder. 

> - From the ivtv driver, now I assume that vbi data is inserted into the
> datastream from /dev/video0 From some time ago, mythtv has been updated
> with some patches that let it record the vbi data into the mpeg file

Yes, I also saw some stuff in cvs that enables embedded vbi in MPEG2, but it 
looks like it doesnot show up in the ringbuffer nuv file or recorded file.
When hexdumping the MPEG files to search for the vbi blocks, I could not find 
the magic words 'ITV0' and 'itv0'. I'm now debugging the mpegrecoder.cpp you 
find out if the problem occurs in the device reading and file creation.

> myth handles. So the last thing needed is to show the teletext on
> screen. I want to work some time on it (well.... not much free time, i

mmm...sounds familiar. But join the group! Any contribution helps.
I also addressed this reply to mythtv-dev, where it belongs...

> must say....), but I will appreciate any help from somebody who knows
> how to do it. In particular, I will appreciate any information of the
> different approaches I can take to show subtitles on myth (OSD, synch
> issues, in which module to work...)
I think we should derive a new OSD class to handle teletext and/or subtitles.
Timing/Sync is indeed an issues; less for teletext but essential for the 
subtitle stuff....
Good starting point is the sources from IVTV and do some reading in vbi code 
and the README.vbi in /doc. You will find how vbi is embedded into MPEG PS 
stream. Next topic is the way how myth treats the IVTV stream. I'm currently 
evaluating this.

Martin