Why don't you calculate them by applying the same transformations as the other runtimes?
You can't possibly interpolate the animations correctly with just world values.
They're always moving as a hierarchy, not as independent bones.
For example, given a child bone that you don't animate, if you rotate its parent, the child will move in an arc.
If you wanted to turn this into world values, you'd have to (1) animate the position of the child too, and (2) animate the world position in an arc. And that's barely half of what the most complicated case is.
