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interesting discovery with sequence frame rates

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Sean Warman
interesting discovery with sequence frame rates
on Sep 14, 2011 at 3:35:37 am

I found this to be an interesting discovery and wanted to share it, and hope to understand it some more.

In an attempt to create my work flow I ran a test with 2 sequences at different settings to determine what was the best choice, and how twixtor handled the difference. It was only for slowmo.

The sequences settings were 29.97 fps and 59.94fps
both were 1280x720 prores 422

The original media is a mix of 23.976, 29.97 and 59.54 fps.
It is all action snow sports.
I am editing FCP 6 on a mac pro tower 8 core

All clips slowed W/twixtor by placing in a nest sequence, then to an interim sequence, then into the final out sequence. The 3 sequences matched in frame rate.
ie. if the final output was 30fps the the nest and interim were also 30fps.
Each clip had its own specific nest and interim sequence.

The interesting part (or at least for me maybe obvious for others):
The 59.94 sequence (with twixtor applied) handled the three differing frame rates very well.
The 29.97 sequence did not work nearly as well, specifically with the footage that was shot at 59.94. Although it did work acceptable with the footage that was shot at 23.976.
is there an obvious reason why?

So, other then long renders and storage is there a problem with editing and exporting on a 59.94 sequence?

Any thoughts or comments are appreciated.

Imagesandconcepts.com


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Peter Litwinowicz
Re: interesting discovery with sequence frame rates
on Sep 14, 2011 at 4:03:34 pm

I'll focus on this question:

[Sean Warman] "The 29.97 sequence did not work nearly as well, specifically with the footage that was shot at 59.94. "

The reason for this is that FCP doesn't let us know the internal clip is 59.94. It forces us to work at 29.97. So what's happening in this case is that Twixtor is only working with 1/2 the number of frames than when you work with 59.94 footage in a 59.94 sequence. Simple as that. Rule of thumb: always work with footage at it's native frame rate. If you need to change frame rates, you'll want to conform the original sequence to the new frame rate first, using CInema Tools. You can follow this tutorial here: http://library.creativecow.net/freitag_lori/twixtor-fcp-frc/1

Your editing the 59.94 footage in a 29.97 sequence is basically a frame rate change, so you'd want to conform to 29.97 first.


[Sean Warman] "So, other then long renders and storage is there a problem with editing and exporting on a 59.94 sequence?
"


No, certainly no problem. HOwever, if you want to edit in 29.97 timeline, you can certainly do that by first conforming the footage you want to Twixtor to 29.97 first.

Pete
RE:Vision Effects, Inc.



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Sean Warman
Re: interesting discovery with sequence frame rates
on Sep 14, 2011 at 6:17:31 pm

Thank you Pete.
I have no preference what frame rate I use in the time line. I am running these test sequences so that understand it and have the best end product.

I have used the cinema tools to do frame rate conversion and very happy with the resulted slow down.

"you can certainly do that by first conforming the footage you want to Twixtor to 29.97 first."
When using twixtor to convert frame rate does it result in a change in speed also?

Thanks

Sean
Shwamy Productions


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Pierre Jasmin
Re: interesting discovery with sequence frame rates
on Sep 14, 2011 at 6:42:21 pm

"When using twixtor to convert frame rate does it result in a change in speed also?"

As Pete said but will repeat with different words so it's real clear,

in FCP 6/7:

the frame rate is effectively controlled by the application settings - the rate at which the video will playback after you render it, X frames per second.

if the original source movie FPS does not match the output FPS of FCP then FCP will skip or double some frames on input. To avoid that you need the Cinema Tools workaround to have the source movie and the output at the same FPS to start. When doing so, the original action is now played slower/faster - and sound would not be synched anymore.

Then you use Twixtor to generate as many frames as you want. Some people use it just to frame rate convert, after the conform step, then you undo it with twixtor (e.g. 30 to 24P, after cinema tools the 30 frames would play slower in 24P timeline, then twixtor 1.25X speed (30/24) will give 24 different frames equally distant in time which might be a better look then reverse telecine sort of thing).

Pierre



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