[mythtv] [experimental patch] Teletext decoder for DVB Cards

Martin Barnasconi mythtv at barnasconi.net
Thu Mar 24 21:17:33 UTC 2005


On Wednesday 23 March 2005 18:25, Frank Muenchow wrote:
> Update the experimental patch for the DVB Teletext.
>
> Changes:
> - included the new patch by Martin:
>      - standard teletext graphics
>      - toggling between transparent/non-transparent background with "W"
>
> - free the processed data packets
>    (sometimes it doesn't work (for me)- see TODO)
>
> - some debug messages can be showed up by starting the frontend with
>    "-v vbi" (Martin: Do you use this as well?)

Ehhh, didnot finish the VERBOSE stuff as you did, but I will add the 
print_verbose_messages in the main routines for mythfrontend and mythbackend 
before launching the next patch.

>
> - bit error detection and correction if possible in page number and
>    line number
>
> - up/down doesn't go wrong when out-of-decimal range

Did some simular stuff to correct this, but your code is less difficult so I 
will copy yours...

> Tj schrieb:
> > The strings with subtitle texts in page->data[y][0] sometimes starts
> > with @....% (where .... are some unknown chars).. What are these?
> > Control information? Do you have this as well, perhaps its just
> > Australia specific? Or my DVB-T (VisionPlus) specific? Is it always 10
> > bytes long?
>
> - fixed
>
> > This patch modified the 1st for loop in TeletextView::drawPage() to skip
> > @....%, and skip drawing the teletext number if it's 801 (probably this
> > patch only works for Australia)... With this, closed captions worked ok
> > on my system (no 'trash' text other than captions). would be nice if it
> > has a black background, still not sure how that's done yet.. Sorry th+e
> > patch is kidda scrummy (my MythTV is our TV and I can only squeeze in a
> > quick fix here and there during commercial breaks)...
>
> I changed this a little:
> - Every subtitle-page (as defined in the page header) skips the drawing
> of the teletext number
>
Instead of blanking the numbers, we should split the drawPage() in a 
drawHeader() and drawPage(). Is is necessary to perform fast updates of the 
header only, to view time or page changes. If we have a separate 
drawHeader(), we can black this easily for subtitle pages.
>
> still TODO:
> - get some wrong graphics in teletext

Is this due to my code or is this related to some different character mapping 
between DVB and PAL TT?

> - sometimes the packets are processed twice (see my last post)
>    (I made a work-around for this, but it's not a good solution)
>    (If somebody has an idea: look at avformatdecoder.cpp, void GetFrame)
>
>
>
> Frank

Guess we should find a better way merge the DVB and IVTV/BTTV  code. The 
line=999 is quick and dirty; I rather see a switch somewhere like 'if 
(mode==VBI_DVB)' etc with switches for VBI_IVTV, VBI_BTTV, VBI_DVB.

Martin


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