[opendtv] Re: Format Independence
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 10 Nov 2005 13:06:40 -0500
At 10:32 AM -0500 11/10/05, John Shutt wrote:
>It has been PBS's experience that MPEG 3:2 pulldown detection does not work
>as well in the real world as it does in the lab.
>
>When PBS first went to Digicipher II distribution of the network feed to the
>affiliates, they had the 3:2 detection in the Digicipher encoder (an MPEG II
>encoder) turned on, thinking that with so many programs originally shot on
>film, we'd save many bits and raise quality.
>
>What ended up happening was that yes, the programs were shot on film, but
>edited in video. So at every scene change the 3:2 sequence was disturbed,
>and the encoder would freeze the image as it went from film mode to regular
>mode, then auto detect the 3:2 sequence again and freeze the image as it
>switched back to film mode.
>
>3:2 pulldown detection has been turned off ever since.
>
Good points. if those scene changes involve a dissolve or special
effect, the source becomes interlaced. And disruption of the 3:2
sequence was commonplace. Things have improve in that area thanks to
DVD authoring.
We tried to amend the MPEG-2 standard to use some reserved bits to
convey the kind of information needed to deal with these problems.
The amendment was defeated because using those reserved bits would
cause some deployed decoders to choke - they just hard coded these
bits never expecting to see them used. So much for an extensible
standard...
Regards
Craig
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