In article ,
Arny Krueger wrote:
Just how much extra compression can you apply and still
call it HD Arny?
AFAIK, there is no standard.
I have worked out some methogologies for estimating the actual amount of
data that my HDTV capture card is processing for various TV shows. There is
at least a 3:1 variation in data rate among network and local programs that
display as a 16:9 picture and are labelled as being HDTV.
It's already a compressed format after all.
It appears that the amount of compression can be controlled locally.
Oh, definitely.
Even for over-the-air signals direct from the studio and transmitter,
you can see quite a bit of variation. Some stations prefer to use all
of their air bandwidth for the primary program. Others send one, two,
three, or even more sub-programs using a portion of the bandwidth.
Satellite and cable companies may also choose to down-sample the
"HDTV" stream to a lower bit-rate, before multiplexing and
re-modulating through their own transmission plants.
One of the big points of contention for cable has been the question of
just what the "Must Carry" rules mean, with respect to HDTV. Is a
cable company required to carry *all* of the program streams sent by a
local broadcaster, or only the primary one? Are they allowed to
downconvert any of the streams to a lower resolution or bit-rate, or
must they carry them as-originally-transmitted?
The locals tend to prefer a "must carry everything, as we transmitted
it" approach. The cablecos prefer a "must carry only the primary
program" approach. I don't think the FCC has issued a final ruling on
the matter.
--
Dave Platt AE6EO
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