[opendtv] Re: Food for thought

  • From: "Bob Miller" <robmxa@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 24 Feb 2007 08:41:11 -0500

Here is a report on Sky's plans to use MPEG-4 and why.

http://www.boinng.com/story/sky-make-a-grab-for-freeview

"By switching to the newer MPEG4 compression standard they'll be able
to squeeze more channels into the same space, but they'll also be
preventing any users with existing boxes from accessing the service,
meaning they'll have to convince people to buy new equipment. They'll
also be in direct competition with Top Up TV, who are already trying
to sell their own "Anytime" service with their own proprietary PVR,
and their own premiership football courtesy of Setanta."

Bob Miller

On 2/23/07, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx> wrote:
Bob Miller wrote:

> 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 that would adjust the numbers downward a little bit for how much Mb/s
are used in each SD channel, and also downward a little bit for the
lowest possible Mb/s they deem adequate for HDTV.

However, I'm not convinced until you show me your source. If you go to
this site:

http://www.dgtvi.it/stat/Europa/Gran_Bretagna/Page1.html

and scroll down to the bottom of the page, you will see a picture of the
Freeview offerings. And a paragraph (in Italian) that describes this,
including the existence of some regional multiplexes.

Freeview channels seem to be divided as follows:

Multiplex 1: 5 streams
Multiplex 2: 5 streams
Multiplex 3: 5 streams
Multiplex 4: 4 streams
Multiplex 5: 4 streams
Multiplex 6: 4 streams
Multiplex 7: 5 streams

Total: 32 program streams.

Now go to the mabb site, to see if this bears any resemblance to what
the Germans determine adequate SDTV quality to be. German DTT is also
16-QAM, so the comparison should be valid.

http://www.garv.de/

shows a similar graphic of the German DTT offerings. Note that these are
a consistent 4 program streams per multiplex, which again suggests that
good 576i quality is achieved at bit rates of around 3 to 4 Mb/s per SD
stream. And the half of the Channel 59 multiplex is dedicated to radio
streams.

Detail: The German scheme used in Berlin needed to increase the GI to
1/8, in order to support their SFN. Therefore, the bit rate available
dropped to a MAXIMUM of 14.75 Mb/s, with a few multiplexes less than
that, which gives each SD stream an average 3.7 Mb/s maximum capacity.
The UK system I'm not positive about, so I assumed the GI to be 1/16,
giving them some extra spectral efficiency.

However you do thes numbers, 3 to 4 Mb/s are the consistent bit rate
deemed adequate for SDTV in 576i. So it always comes out to 9 to 16 Mb/s
required for H.264 HDTV quality, by BBC's own reckoning (not mine).

Bert


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