On Sunday 13 February 2005 22:21, Martin Barnasconi wrote:
> During the development of some embedded vbi decoding stuff for mythtv,
> I think I found an "offset" of 8 characters between the data in the true
> sliced vbi stream and the embedded stream.
> Note: looks like its the data only, not the ID fields marking telelext,
> vps, wss,etc
> Here some output:
> modified /utils/vbi.c (grabs /dev/vbi):
>
> WST 7 20 326 >/..-.Beweegbare deel Fonejachtbrug: <
> WST 7 21 327 >j. .- Max.breedte 9 m tot apr. <
> WST 1 31 330 >Gj!8jjjjjj*. Nozema Datacasting ..<
> WST 7 24 331 >/!.volgende .nosnieuws .index .nossport <
> WST 6 00 332 >8.jj}....G.NOS-TT 721.zo 13 feb 21:13:54<
> WST 7 00 333 >/.IIdP..IG.NOS-TT 722.zo 13 feb 21:13:54<
>
> myth-routine (same algorithm, grabs embedded vbi)
> WST 4 25 021 > ...GG...ddG.NOS-TT 199.zo 13 feb 1<
> WST 4 08 631 >$D..u+.8.jj}....G.NOS-TT 254.zo 13 feb 1<
> WST 4 16 644 >[EMAIL PROTECTED]&,Fq7...H)Oroh&..............h...<
> WST 1 02 645 >.......p..tuV..]WB0([EMAIL PROTECTED],.`"....'[EMAIL PROTECTED]<
> WST 1 12 647 >.0.......k...............Db...... [EMAIL PROTECTED] <
> WST 7 31 007 >jj/j)z... . (,,|4| h4 ,,l| |,|h<<|. . <
> WST 4 25 021 > ../.22.37 .boekenwijzer <
> WST 3 20 631 >^.S}.0.IG.00.02 .met het oog op morgen <
>
> See f.i the line containing "NOS-TT". This offset distroys my header and
> magazine info totally to do proper decoding
> Yes, I can add a +8 offset to the buffer, but this means that the last line
> is not usable (I will miss 8 chars then).
>
> Could someone familiar with IVTV vbi sources check if this data offset is
> generated in the encoding part?
Using 0.3.2c it all looks fine. What I did to test it (only works with a
PVR-350) is to enable embedded teletext (ivtvctl -x 1 -b teletext), then run
'cat /dev/video0 >/dev/video16' and then run 'util/vbi /dev/vbi4'. vbi4 is
the device that outputs the embedded VBI data. The PVR-350 is responsible for
extracting it from the MPEG stream, and the driver transforms it to the same
format as /dev/vbi0. Both /dev/vbi0 and /dev/vbi4 are OK here. So I suspect
your code that extracts the embedded data.
The code in ivtv-vbi.c, ivtv_DEC_VBI_fixup() shows how to interpret the
embedded data. You can also mail me your code if you want me to look over it.
I wrote the ivtv VBI implementation, so I daresay I'm familiar with it :-)
Hans
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