[opendtv] Re: Food for thought

On 2/22/07, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx> wrote:

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.


But they actually "pack" 9 program channels in on 64 QAM channels..
They may only be doing 8 today but they consider then that they have a
spare unused for sale slot available. With 16 QAM they "pack" 6
programs channels in and again if they are not using one or two those
slots are for sale, up for grabs.

So it is some part of those numbers, 9 or 6,  they are talking about
losing if the substitute HD program channels.

If they displace 3 SD programs with 1 HD program using MPEG-4 then
there is room for 3 HD programs in a channel using QAM 64 or any
combination of SD and HD that fit, 2HD/3SD for example. Of course this
is silly since they will use MPEG-4 for the entire channel and that
mix would be more like 2HD/6SD especially with the help of statistical
multiplexing that this many program channels would make very useful.

Similar math if they displace 4 SD programs with 1 HD program.

So they would lose I program channel per multiplex using MPEG-4, QAM64
if they inserted 2 HD and 6 SD program channels displacing 6 SD MPEG-2
program channels.

And they would lose 5 program channel per multiplex using MPEG-4,
QAM64 if they inserted 2 HD and 2 SD program channels displacing 9 SD
MPEG-2 program channels.

So whether an HD MPEG-4 program channel displaces 3 or 4 SD MPEG-2
program channels is a big deal.

Mux 2 is using all 9 of its slots at the moment.

Bob Miller


.



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


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