Bob Miller wrote:
Your logic seems to say, if I understand it, that is by
switching to MPEG-4 and doing HD only they will sacrifice
3 or 4 SD MPEG-2 program channels per HD program channel.
Yes, that is what the BBC wrote.
Following that logic though you could do 2 HD program
channels with MPEG-4 and have either 3 SD or 1 SD program
with MPEG-2 also.
In a 23.42 Mb/s channel (64-QAM, 2/3 FEC, 1.16 GI), the BBC would be
able to pack anywhere from 6 to 8 SDTV streams, since these SD streams
are average 3 to 4 Mb/s.
Instead of 6 to 8 SD streams, in that same 8 MHz channel they could
transmit 2 HDTV streams. They did not give an actual range of bit rates
for HDTV, only stated that 19.5 was the maximum. The important point
that everyone prefers to ignore, but only using words and never
numbers,
is that this is not substantially different from MPEG-2. I'm sure
the HD
would be subjectively better with H.264, but we are NOT talking about a
big difference, *from what they report*.
If we assume that "3 to 4 SD streams" can translate to 9 Mb/s for HDTV
H.264 as a very bare minimum, then in the 23.42 Mb/s you could
potentially transmit two HD streams and have 5.42 Mb/s left over for
SDTV. Again, not substantially different from MPEG-2, where you can
also
use an average of ~9 Mb/s for a 24p HD stream, as a minimum.
But if you went completely to MPEG-4, then you could have
the 2 HD program channels and 6 or 2 SD program channels
also
They didn't say what SD bit rates were possible with H.264. But from
the
Sky comment, you might say that 5.42 left over b/s (from two bare
minimum HD streams) could either be used for 2 SD streams with MPEG-2,
or 3 SD streams with H.264. But these would be low quality SD, less
than
3 Mb/s for MPEG-2.
This is everything at the bare minimum. If the HD streams were sports,
for instance, or one of them was, you wouldn't have this option.
Bert
