Final Cut Pro FCPXML precision issue with effect parameters

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Level 4

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Final Cut Pro FCPXML precision issue with effect parameters

FCPXML effect parameter value storage seems to have a precision problem.

Background: I am building tools (Claude skills and python code) that use FCPXML exports of multicam interviews and transcripts to programmatically generate projects. This project FCPXML references the original multicams via the exported multicam FCPXMLs so when a generated project is imported into the library, it uses these already existing multicams. Nice and clean and works great.

A curious thing I ran into recently is that one particular interview multicam (out of six) would always be recreated when importing the project FCPXML. This multicam was a bit unusual with Gaussian Blur and Glass Block effects applied to obscure the interviewee.

What I discovered is if there is an effect parameter that's altered via the slider, like the Glass Block's Center, the internally stored value appears to exceed the FCPXML's 6(?) digit precision. Using that multicam's FCPXML export to build the project FCPXML resulted in FCP creating a duplicate multicam on import because it considered the mutlicam referenced in the FCPXML to be different than the one in the library.

Even stranger, if I reset the Glass Block effect values using the UI dropdown menu, it still duplicated on import. Resetting Glass Block apparently also writes values that exceed the precision of the FCPXML. If I removed and reapplied the effect without making any changes, then it was not duplicated on import. No effect parameter values are written in the FCPXML on the effect if there were no changes. Or, if I manually entered a value into the field versus using the slider, then it would import without duplicating.

I reported to Apple Feedback but probably only an issue for those of us leaning on FCPXMLs for workflows. Just curious if anyone else has experienced this.

Posted on Sep 22, 2026 2:20 PM

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Answer 1

fox_m

Level 6

13,716 points

Sep 22, 2026 7:35 PM in response to terryb

I'll preface this with I know very little about FCPXML.

A Motion template is only XML (ozxmlscene subtype).

If I had to guess (and I am only just guessing): Final Cut loads the FCPXML and the Motion Template XMLs all together.

There are two layers of Parameter values in Motion: those you see in the interface, and those Motion maintains "under the hood".

Motion's precision is 16 decimal digits (you can see it in template XMLs).

The 6-decimal values you see in the FCPXML are *probably* for the Slider "offsets" used inside FCP and not the underlying Motion template values. If (and I don't know this for myself) the Motion Template XML is "read into" the FCPXML, you may also see the 16-decimal values for the template.

(I obviously don't know how this works... Just guessing). I also don't know *how* you are "resetting" Glass Block parameter values.

If you see values for Glass Block that don't make sense with respect to its parameters, again, what you see in the (Motion) interface is not always what's going on "behind the scenes". All rotations behind the scenes are in Radians translated to Degrees (what you see.) Position values may have aspect correction scaling. Stuff like that. If you're trying to set values that "don't make sense" to Final Cut, it may simply be resetting them to "defaults". (Again, just guessing.)

Does any of this help?

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