[opendtv] Re: Food for thought

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 23 Feb 2007 16:51:24 -0500


Although I think I'm overstuffed with all this food for thought, I would like to point out that even in the worst case scenario of a 30 frame GOP MPEG structure, an I frame comes along once every second for 30 FPS and once every 1/2 second for 60 FPS video.

We don't use anything longer than a 15 frame GOP for our stuff, and I don't know of anybody else who goes longer than 15 either.

Tuning delay is not related to MPEG GOP structure.

As for your HD Radio tuning delay from the main channel to the secondary channel, look to your particular radio for the explanation (or the chipset it uses) of the 5 second delay in tuning a subchannel, not for anything inherent in the HD format.


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

Indeed, and this is a sensible point, IMO. For sure, encoders will
improve, as MPEG-2 encoders have. But I still think that practical
deployed systems will have to operate at less than their theoretical
ideal, simply because of the sync-up time problem.

A somewhat unrelated example is HD Radio. If you tune to a primary
channel, which comes also in analog, the tuning experience is fine. The
analog comes in right away, the digital seamlessly replaces the analog
in a few seconds.

Try tuning immediately to a subchannel, which has no analog equivalent.
I just don't think that kind of delay can be acceptable, in an
all-digital radio. The wait must be more than 5 seconds. I don't think
DTV tuning would be considered acceptable with that sort of delay
either, yet that is the primary mechanism which provides the codec
efficiencies (when quality is kept constant).

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