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RE: 1080 at 24P HD Frame Rates



Mark wrote:
	Could you clear up for me what exactly the 24/1.001 or 60/1.001
frame rates
	are that are mentioned in the 1080 at 24P document?

	I am guessing they are 23.976 and 59.97 fps (current US telecine
playback
	and NTSC TV signal frame rates, respectively), but why the new
method of
	writing?

They are indeed 23.976 and 59.97.  The reason for expressing them this
way is that you can work out to many significant decimals the actual
running speed, necessary for designing the various pieces of equipment
to a given standard.
Please also note that many manufacturers supporting HD rates (SDL
included) are also supporting true 24 and 60 as well as the 'drop frame'
rates and this is in turn is going to lead to some problems with
nomenclature and practice.  
Indeed it is very hard not to say "24" when you mean 23.976, but as the
default will be 24/1001 so perhaps 24 will eventually always mean 23.976
and we will have to say "true 24" when we mean actual 24 frame all the
way.   
At this time, most of the 1080 transfers I have seen have been done at
true 60.  This is probably due to the legacy of older HDTV equipment.
But the 59 / 60 is easier as you can state "59" or "60" and we all know
what we mean.  This is be the way it is already going.
The 24 frame progressive transfers that we have done so far have all
been at 23.976 but we have played them out at 24 and 59.94 (and 60)
interlace (by adding 3:2 pulldown) and even 25 (when its 25 its always
25!), which is the normal speed up as seen in SD Telecines. Perhaps we
should also note that 23.976 has been in use in standard definition in
the States for sometime, mostly used in mastering for standards
conversion.  
24 FPS 1080 makes the most sense as a universal mastering standard at
HDTV rates as from there you can make almost any of the proposed
standards with the least artifacts.  
I think I could claim a record for the most use of the word 'standard'
in an email reply for which I apologize.

Steve Roach
Product Marketing Manager
Sierra Design Labs
999 Tahoe Blvd., 
Incline Village, NV 89451
Voice; 702 831 7837 Fax: 702 831 5710
http://www.sdlabs.com
stever at sdlabs.com



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