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Old May 20th, 2014, 06:57 PM   #1
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24p (sort of) into 60i file without any 3:2 pull-up

Normally when 24fps film is converted to 60i video the telecine adds 3:2 pulldown.

I have my own telecine that converts one film frame to one video frame--the two fields come from the same film frame. Thus, in 30 frames there are 24 frames plus 6 more. (So it's 30p in 60i.)

When I drop such a 60i clip into a 23.98 Timeline in FCP X -- it immediately starts processing the clip. (I can also use the Conform function, but it's not needed.)

I wonder exactly what FCP X is doing. My guess is that it looks at the 59.94i clip -- it's DV -- and the 23.98p Timeline and decides the right way to handle this is to take the 60 fields and use Inverse 3:2 pulldown to get 24 frames. Does this sound correct?

Because the 60 fields hold 30 frames of film, the result in the 24p Timeline should not play at the right speed. Correct? Except it looks fine on playback!

I'm wondering if I'm doing the conversion math right. If 30 film frames -- which is 1.25 seconds of film -- become 24 video frames that play over 1.00 seconds, then it seems like the running speed is 25% fast. Does this sound correct?

Unless as fields are re-distributed during the inverse pulldown, some are dropped. Every time 2 fields are dropped, the playback speed becomes less "too fast." Were 12 fields dropped -- then 6 frames would be eliminated -- so the result wouldn't run fast. Can some genius confirm or deny this theory of dropped fields during 3:2 inverse pulldown. Thank you.


In a series of 5 video frames, it looks like the Odd field in Frame 3 and the Even field in Frame 4 are dropped. Thus over 6 segments of 5-frames each, drops 12 fields which is 6 frames. The first 2 film frames (A, B) and the last film frame (D) are passed through in each group of 5 frames. Frame C is a split or judder frame which has fields from different film frames. Thus, there are 6 judder frames per second.


PS: if I telecine 18fps film, drop it in a 24p Timeline, export it as a 24p movie, import it as 24p, and then slow the result by 25%, it plays fine too. It would be nice if one could tell FCP X that the frame to discard to slow playback by 25% would be the split/judder frame. I have no idea how FCP X slows down playback.Does Apple document how FCP X does what it does?
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Last edited by Steve Mullen; May 20th, 2014 at 09:07 PM.
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Old May 20th, 2014, 08:52 PM   #2
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Location: New York City
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Re: 24p (sort of) into 60i file without any 3:2 pull-up

FCPX does a very good job at frame distribution when you drop a clip of differing frame rates into a project. The program's default mode is to maintain time over frame count. Dropping frames is one way the program deals with higher frame rate files in lower rate projects. You can try other methods that merge frames but this can cause mushy movement. Generally dropping frames is more visually problematic than adding frames as in when placing 24p into 60i for example. Conforming the frame rate will introduce speed effects such as a slight slow motion and the audio will be pitched lower. In PAL land, it has been normal practice to conform 24p to 25p for television, adding a frame every second doesn't look very good, which speeds up films so running times are different.
William Hohauser - New York City
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