OT: Composite/Component [was Re: [mythtv-users] Re: Image quality,
what effects it?]
Jay R. Ashworth
jra at baylink.com
Fri Aug 13 15:08:23 EDT 2004
On Fri, Aug 13, 2004 at 08:31:54PM +0200, Rudy Zijlstra wrote:
> >Yeah. The PcHDTV card is probably doing that.
> >
> No, it is not. It is receiving a 2, 4, 8 or 16 VSB modulated MPEG-2
> Transport stream according to the ATSC standard and selecting the wanted
> PIDs out of it.
Oh, of course: that card has to *decode* MPEG, which is (by design)
much easier.
> SW support is only for 8-VSB (the only modulation currently used on
> ATSC), which limits the TS to 19.4 Mbit/s. This means the card is
> specific for terrestrial ATSC. On a cable the signal is likely to be
> re-modulated in QAM-64. QAM-256 might also be used. Most cable companies
> use QAM for digital modulation and will not support 2 different
> modulation schemes at the same time. Also the ATSC standard (at least
> when last I looked at it) does not mandate any particular modulation
> when used over cable. For terrestrial use VSB is mandated. Sattelite
> uses QPSK (QAM-2) modulation.
I believe SCTE-40 specifies QAM-64, yes. I do wish someone would do a
card.
And this a-la-carte cable crap...
Cheers,
-- jra
--
Jay R. Ashworth jra at baylink.com
Designer Baylink RFC 2100
Ashworth & Associates The Things I Think '87 e24
St Petersburg FL USA http://baylink.pitas.com +1 727 647 1274
"You know: I'm a fan of photosynthesis as much as the next guy,
but if God merely wanted us to smell the flowers, he wouldn't
have invented a 3GHz microprocessor and a 3D graphics board."
-- Luke Girardi
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