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Discussion Starter · #1 ·
The dumb question of the day: Why are the ATSC formats 1080

at 24p and 30p not used ? Most film based material, as I understand,

is converted from 24p anyways, so why not use those formats ?
 

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Quote:
Originally posted by S. A. Moore
The dumb question of the day: Why are the ATSC formats 1080

at 24p and 30p not used ? Most film based material, as I understand,

is converted from 24p anyways, so why not use those formats ?
First there is no 30P, it's 60P. 30P would flicker. The reason for lack of 24p broadcast is NTSC compatability. In fact it's really not 24 or 30 either. It's 23.97 and 29.97. This is because in NTSC the vertical rate is 59.94hz not 60hz. The reason is the complex interleaving of the chroma carrier.

Running a 24P HD operation within a broadcast facility still running NTSC presents too many problems with timing, that is clock on the wall timing. These problems could be solved but it's not worth the time and money.

The television industry wants to go back to even integer frame rates and hopes to do so once NTSC is dead. It would make life so much easier. At that time it would be possible to operate at 24P.


Another problem today is no consumer STB has been fully qualified at 24P. Even though this is an ATSC table 3 standard, it's not sure how the population of STB's would react.
 

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Discussion Starter · #3 ·
Quote:
Originally posted by Glimmie



First there is no 30P, it's 60P. 30P would flicker. The reason for lack of 24p broadcast is NTSC compatability.
The're ATSC standards. See the standard site for the ATSC:

http://www.atsc.org/standards/a_53b.pdf


Yes, 1080 24p and 30p DO exist.


Point taken on the flicker, but of course that problem does not exist

with a lot of TVs, since they buffer up the frame. There are a lot

of sets out there claiming to support all 18 formats. What would they

do with the 30p formats ? Not display it ?
 

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All the DTV-stations in my area broadcast have a single chosen format. I've never seen a station which broadcasts in one format (like 1920x1080 30i), then switch to a different format in order to broadcast a movie (like 1920x1080 24p.)


On network TV, most commercials are produced in 60i format...this is my conclusion after seeing D-Scaler rotate phase on practically every scene transition. A lot of 'film-like' primtime-TV programs also exhibit 'rotating 3:2 phase' (sorry, is there a proper term for this?)


In order for *any* 24p broadcast to be practical, I think all source content needs to be fully 24p aligned. But from what the industry folks here have said, lots of TV-programming is shot principally on film, then "finished" on video. And the perfect 3:2 pulldown is lost somehow during the process.


So even if a TV-station rotated between two formats (say 30i for advertisements and news-shows, and 24p for primetime program content), a lot of programming-content doesn't seem to have perfect 3:2 pulldown.


I've also noticed many TV-networks modifying the presentation of movies in not just the 2-D (aspect-ratio) composition, but also the 'third dimension', or 'temporal stretching'! ABC really likes to stretch its Saturday/Sunday movie presentations! At least, it seems that way because D-Scaler can't lock and maintain a 3:2 pulldown. I conclude the film's original 24fps academy rate has been increased/decreased to fit a 2-hour time-slot.

(Sixth Sense, Armageddon, October Sky, the Bond Picture Show -- these were all compressed/stretched, coming out KABC/7 Los Angeles. On the plus side, a few movies were presented with no temporal-stretching, like Stuart Little.)


Broadcasting a 'temporally stretched' film in a 24p format would look *awful.* Every second or two, the picture would freeze or skip noticeably. I wish some Hollywood producers would enact a 'Temporal Prime Directive', which prohibits compression/expansion of film lengths.


^^^ disclaimer, all statements of fact above should be taken with a grain of salt until arm-chair technical commentaries have been deemed authoritative!


Glimmie, mmmost, did what I write make any sense?
 
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