Currently, FBX imported animation sequence data can use one of two kinds of interpolation within the sequence: stepped and linear. But wit this setup, if the user has an animation that needs to use a mix of both linear and stepped interpolation, they can’t.
Importing animations in Unity by default allows for the mix of stepped and linear keys in one animation. It’s a very useful feature for doing advanced character work (e.g. the immediate scaling of joints for visibility purposes). The user doesn’t have to worry about how the animation will play at lower time scales either – the linear and stepped key behavior will always be intact no matter how slow the playback rate is. This is especially good for replays or other time scaling systems.
It would be ideal if the Unreal importer could parse which keys are linear and which are stepped and set them in the sequence accordingly.