Unable to import custom tangents from an FBX animation source

Development Character & Animation
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1

Hello there,

It seems that we can’t retrieve the tangent angle, weight, or tangent mode from transform keyframes when importing an FBX animation source file. The available interpolation modes appear to be limited to linear or step, and they are applied to all keyframes globally.

I can’t find a way to get the values contained in the source file.

Example of source animation curves from the FBX file (Maya):

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Interpolation mode seems to override tangent values:

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Am I missing something here, or is this a limitation of the engine’s FBX importer?

Thanks, and have a nice day.

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2

Steps to Reproduce
In a DCC (tested in Maya 2025), create a primitive and animate it with a single keyframe set to step mode.

Export the FBX.

Import it into Unreal Engine.

Notice that the animation does not preserve the step tangent you set.

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3

Yes, this is correct: all keys stored in anim sequence files are considered linear or stepped keys globally. We don’t store non-linear tangent data like this in anim sequences; only material/additional curve data and sequencer curve data, for optimization purposes.

This means that you can’t mix and match that curve data at the moment.

Dustin

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4

Alright, thanks for the confirmation. Have a nice one!

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