[mythtv] [experimental patch] vbi decoder for IVTV cards

Stutty stutty at gmail.com
Wed Mar 2 19:26:01 UTC 2005

Got the patch applied now thanks, first impressions of actual decoding
is very good. Current issues I have, sorry don't have time to
investigate much, but thought you might like the feedback:

Using Hauppauge PVR-350 for recording, playback using EPIA TV-out
(Unichrome & Software).

So the only relevant one may be:

1) 888 subtitles are not 100%, this could be reception issues -
difficult to tell, however my picture is crystal clear and other txt
pages I tried did not present any typical bad reception type errors.

Other comments (This is my first experience of TText on Myth so these
comments may be more general?)

2) Text fonts/colours (obviously only grey scale when using
Unichrome), I presume just a matter of tweeking the theme? But when
using software decoding impossible to read without contrasting

3) OSD offsets do not work for me, so text is often off the right of the screen.

4) Using XvMC_VLD Unichrome decoding, has the usual performance issues
with heavy use of OSD - but then this has nothing to do with your

Anyway must dash,


On Tue, 1 Mar 2005 22:47:58 +0100, Martin Barnasconi
<mythtv at barnasconi.net> wrote:
> Here the first experimental patch for the vbi decoding for PVR cards using the
> IVTV drivers. Although its far from perfect (that's why it's classified as
> experimental;-) it gives you some idea how things are implemented and I
> challenge you to contribute to fill in the missing gaps or to improve the
> code.
> What it does:
> it relies on having embedded vbi in the MPEG stream as defined in the IVTV
> doc's. The embedded vbi stream includes the magic cookies "itv0' and 'ITV0'
> to mark the beginning of a vbi private stream. That's why some additional
> lines are added to the avformatdecoder and ffmpeg decoder classes, to
> recognize a vbi data steam. If detected, it will start decoding in the
> vbidecoder class. An additional OSD overlay osdtypeteletext is used for
> teletext and subtitles. Whole process is controlled from tv_play routines.
> Pages are updated after receiving new content, so even subtitling pages (e.g.
> 888) do work!
> What it does not do yet (TODO ;-)
> - It overrules the 'T' key for teletext/CC for non-encoder cards
> (bttv/saa7134) . The original vbi code (part of nuppelvideoplayer/recorder)
> is still in, but I rather see this becoming part of this new vbidecoder
> class. Like to see 'C' for CC/subtitles and 'T' for teletext. Problem: 'C'
> function already in use...
> As some people have a mixed PVR/bttv setup, we should detect which card is
> operational and select the correct vbi decoder.
> - CC is not working yet, as we do not have this here in Europe. Please test
> the results in ccbuffer and in your stderr terminal and please report your
> findings.
> - Teletext is text-only. No mosaic or other fancy stuff like blanking, FLOF,
> blicking, reveal functions yet. Uses current CC_font in OSD. Should be
> teletext font in future. for the OSD overlay, we suffer from the color
> mapping of YUV420 here. Use a font with sufficient width (eg bold fonts) to
> be able to read the blue or red text.
> - other embedded data like WSS/PIL/CNI/VPS/PDC captured but not used.
> Framework in place, detection and corresponding actions (e.g. signals and
> slots) to be defined.
> - TT OSD overlay is now transparent. Future work is to have black,
> transparent, or even left-TV/right-TT (for 16:9 screens) or TT-PIP
> implemented (for big screens)
> Give it a try and report your findings. Improvements are very welcome.
> Martin
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