[opendtv] Re: Food for thought

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 21 Feb 2007 12:41:43 -0500

----- Original Message ----- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>

The BBC claimed, from their real-world testing, that this many SD
programs would have to be removed to make room for one H.264 HDTV
program. That looks to me very much like a low estimate of 12 Mb/s, and
a high estimate of 20 Mb/s. Throw whatever prefiltering words you like
at this, the results are not a dramatic improvement compared with H.262.
As I already said, I do not doubt that H.264 will give better results as
the bit rate is reduced.


If you want to play quote games, then I hope you didn't miss this quote from the BBC presentation:

"HD set-top boxes were specifically commissioned and developed for the trial by Humax and ADB. These operated using the MPEG-4 compression standard rather than the MPEG-2 used in standard DTT boxes, allowing more efficient encoding of the broadcast signal. This was essential to the successful delivery and decoding of the HD signals used in the trial, and meant that any households with standard DTT boxes were not able to view the HD services."

You don't know what subjective quality standards the BBC were using to determine that 19.5 Mbps MPEG-4 was the minimum acceptable bitrate. For all you know, if they used MPEG-2 like we do here in the US, they might have determined that 40 Mbps was the minimum acceptable bitrate.

Digital encoding is not a cliff edge, it is a continuum. As you vary the bitrate, you subtly vary the amount of video impairment according to the scene being encoded. At 18 Mbps I see scenes from PBS with macroblocking. Would this have been unacceptable to the BBC? You don't know, therefore you cannot intelligently make the assertions you made from that single sentence you quoted.



I'm just after some unvarnished truth, rather than press releases.

Now you sound like me back in August of 1999!

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