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How exactly does 24p pulldown removal work? (get technical, please)

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Scott Smitelli
How exactly does 24p pulldown removal work? (get technical, please)
on Oct 5, 2009 at 1:53:34 am

I've been using FCP's automatic pulldown removal for what seems like an eternity, but I've never given much thought to how it works... until now.

In a nutshell, how does Final Cut determine which frame the pulldown cadence starts on? Is it written to the metadata on the tape (with the timecode, date/time, user bit, etc) or do all 24p cameras adhere to an unspoken convention to always start the cadence on frame :00, :05, :10, or similar?

If a DV tape is dubbed onto another tape, can FCP always detect the cadence on the new copy? What about if the tape was dubbed via an analog Composite jack?

When FCP removes Advanced pulldown, it simply gets rid of one frame out of every five... Is this extra frame ever saved in the .mov file on disk (perhaps with a flag saying "skip over this frame") or is it always discarded outright? Source footage from, say, a DVX has timecode with frame numbers ranging from :00 to :29, but with 6 frames each second skipped. Are those frames still in the QuickTime file somewhere?

Does any program in Final Cut Studio (especially Cinema Tools) do any type of image content analysis to try to intelligently locate interlaced frames? Why is it that sometimes Cinema Tools can detect a non-Advanced pulldown cadence on its own, yet other times I have to manually tell it?

I've gotten so used to the "it just works, except for the few times when it doesn't" mentality. I'd like to someday be able to figure out WHY it doesn't work those times. ;)


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Bouke Vahl
Re: How exactly does 24p pulldown removal work? (get technical, please)
on Oct 6, 2009 at 7:04:15 am

Most pulldown removers use TC to find the cadence.
In Avid, you can set cadence start. No idea about FCP though.

It is possible to detect the cadence in software (i made such a thing years ago), but you need to have a fair bit of motion in the shot or it does not work.

Next, there is a huge difference in Advanced Pulldown and normal pulldown.
Don't let the nake fool you, advance pulldown is easier to remove, as it creates a new interlaced frame that simply can be kicked out.

Normal pulldown adds a FIELD every now and then, merging it with a unique field.
Both an be removed without quality loss, but removing normal pulldown is a bit harder.

Advanced pulldown is ideal for shooting when the carrier is a NTSC system, normal pulldown is ideal for end use (dvd/broadcast)



Bouke

http://www.videotoolshed.com/
smart tools for video pro's


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