[opendtv] Re: Case for 720p60

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Tue, 20 Apr 2010 08:58:19 -0400


----- Original Message ----- From: "Craig Birkmaier" <craig@xxxxxxxxx>

In ATSC-land, where there are no MPEG-2 MP at ML restrictions, in principle at least, broadcasters could begin to transmit SDTV as 480p24 or 480p60. So why don't they?

The only 480p format that could be used is square pixel 640 x 480 with a 4:3 aspect ratio. The ATSC does not support 854 x 480p or 704/720x480p. These formats are supported by MPEG-2 at various levels, but there is no guarantee that all ATSC receivers will display them, so broadcasters do not use them.

Craig,

I believe you need to re-read table 6.2, Compression Format Restraints, contained in A/53 Part 4, 7 August 2009.

True, the ATSC has never supported 854x480P 16:9, but then there is no production gear that supports this resolution, either. However, the ATSC does support 704x480 16:9 progressively scanned at 23.976, 24, 29.97, 30, 59.94, and 60 frames per second.

These 480p widescreen formats have been part of ATSC ever since the infamous "Table 3" (which has migrated to table 6.2) was first issued by the ATSC, and subsequently rejected by the FCC.

We seriously contemplated broadcasting 480p59.94 16:9 for our subchannels that derive from HD source content. I even asked for assistance on this reflector. Our main stumbling block was there is no defined way to feed that format to our encoders. SDI doesn't have enough bandwidth for 480p60, and HD-SDI doesn't included 704x480p60. Further, we tried Miranda, Ensemble Designs, and Ross, but could find no vendor capable of supplying a 1080i30 or 720p60 to 480p60 downconverter. All downconverters wanted to output 480i30.

At the dawn of ATSC, Fox stood alone in choosing 480p59.94 for broadcast, but they soon switched to 720p, probably because they had the same problem finding suitable equipment for the format, and they were losing the "genuine HD" P.R. war.

John




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