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

Staffan Pettersson staffan.pettersson at sverige.nu
Wed Mar 2 21:21:51 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
> background.
> 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
> patch.
> Anyway must dash,
> Paul
> 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
>> 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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Can this be implimented for dvb to? I't would be great if someone make
this work, many channels of my provider sends teletext subs.


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