We now have the following error that is generated in FFbxImporter::ValidateAnimStack

	if (!FMath::IsNearlyZero(SubFrame, KINDA_SMALL_NUMBER) && !FMath::IsNearlyEqual(SubFrame, 1.0f, KINDA_SMALL_NUMBER))
		AddTokenizedErrorMessage(FTokenizedMessage::Create(EMessageSeverity::Error, FText::Format(LOCTEXT("Error_InvalidImportLength", "Animation length {0} is not compatible with import frame-rate {1} (sub frame {2}), animation has to be frame-border aligned."), FText::AsNumber(SequenceLengthInSeconds), TargetFrameRate.ToPrettyText(), FText::AsNumber(SubFrame))), FFbxErrors::Animation_InvalidData);
		return false;

However, we always hit this error for animations that were generated with fractional framerates (like 29.97/NTSC). This is because the FBX import code assumes that framerates can be stored as an int rather than float/double (FFbxImporter::ImportAnimations):

			// For FBX data, "Frame Rate" is just the speed at which the animation is played back.  It can change
			// arbitrarily, and the underlying data can stay the same.  What we really want here is the Sampling Rate,
			// ie: the number of animation keys per second.  These are the individual animation curve keys
			// on the FBX nodes of the skeleton.  So we loop through the nodes of the skeleton and find the maximum number 
			// of keys that any node has, then divide this by the total length (in seconds) of the animation to find the 
			// sampling rate of this set of data 

			// we want the maximum resample rate, so that we don't lose any precision of fast anims,
			// and don't mind creating lerped frames for slow anims
			int32 BestResampleRate = GetMaxSampleRate(SortedLinks);

			if (BestResampleRate > 0)
				ResampleRate = BestResampleRate;
Steps to Reproduce
  1. Attempt to import the attached FBX file (29.97fps)
  2. In the import options, make sure 'Use Default Sample Rate' is unticked and 'Custom Sample Rate' is 0 to ensure we use the FBX sample rate
  3. Import the file
    1. You should get an error about the frames not being accurate

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ComponentUE - Anim - Runtime
Affects Versions5.0.3
Target Fix5.5
CreatedAug 24, 2022
UpdatedDec 18, 2023