On Sunday 20 March 2005 20:55, Martin Barnasconi wrote:
> while decoding vbi lines embedded in MPEG PS, I noticed missing packets
> once in a while. After checking my own decoding routines, capturing each
> line correctly, I started to debug the incoming MPEG PS stream
> (/dev/video); looks like they are already missing here...
> After some tests, I suspect it's in the embedding option to enable VPS:
>
> ivtvctl -b teletext,wss -x 1 (no VPS) and
> cat /dev/video |hexdump|less gives:
>
> 004A9CA0: 05 4E 84 80 07 21 84 85 F1 77 FF FF 69 74 76 30 .N...!..qw..itv0
....
> 004A9EA0: 31 B0 31 20 20 31 B0 32 07 1C 9D 01 46 E5 F2 6E 101 102....Fern
>
> ivtvctl -b teletext,wss,vps -x 1 (VPS enabled) and
> cat /dev/video |hexdump|less gives:
>
> 0066EB50: 07 21 8D DB CD 05 FF FF 69 74 76 30 FE F3 FB CF .!.[M...itv0~s{O
.....
> 0066ED20: 20 31 B0 31 20 20 31 B0 32 07 1C 9D 01 46 E5 F2 101 102....Fer
>
> Both present page 0x100 of dutch teletext. The non-VPS (upper) hexdump
> contains packet 8 containing "RUBRIEK INDEX". In the VPS (lower) hexdump,
> this packet/line is missing.
>
> Is there some dependency between VPS and Teletext such that things are
> overwritten/ignored?
Yes. Selecting VPS means that line 16 is reserved for VPS. There is no
autodetect whether the line is actually teletext or VPS, it is just
hardcoded. The reason is that you have to program the saa7115 in advance with
the correct decoding type per line.
It would be nice if the API would be improved to allow more flexibility. I
have several ideas about it, but haven't had the opportunity to continue with
it.
Hope this helps,
Hans
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