When glTF export in Blender2.8, an animation is not played well When glTF export in Blender2.8, the parameter of the rotary animation of the glTF file turns into the expansion and contraction.


I make the animation which turned a simple early cube.This does 1 rotation in the y-axis.





glTF exports in this parameter





A cube does not rotation when I confirm animation of glTF in this glTF viewer and expands and contracts. 




glTF viwer

This thinks that an export sentence of blender has a problem, will there be the solution?
The movement and the scale succeeded. Only a rotation becomes strange.

file
https://www.dropbox.com/sh/yqbxmrg68m8evwm/AAAbvbYb_00VDH8wbs0rhicEa?dl=0
This should be fixed in the next version of Blender's glTF exporter, where the default value for Always sample animations has been changed to true (in #706).  I believe putting a checkmark on this option may be a quick fix for your problem.

Animations involving rotations are stored in glTF using quaternions (because glTF is a runtime delivery format, meant for rapid load-and-render operations with minimal pre-processing by the loader).  But quaternions have an important limitation, they can't distinguish between +180 and -180 degrees.  If you have Euler angle keyframes at 0 and 360 degrees, both of those values convert to the same identical quaternion, because the object is in the same orientation.  Interpolation between keys breaks down.

The usual solution is to place intermediate keyframes at 90 degree increments (or no larger than 120 degree increments).  One way to do this is just check Always sample animations which makes every frame a keyframe.