  This paper introduces a novel data-driven motion in-betweening system to
reach target poses of characters by making use of phases variables learned by a
Periodic Autoencoder. Our approach utilizes a mixture-of-experts neural network
model, in which the phases cluster movements in both space and time with
different expert weights. Each generated set of weights then produces a
sequence of poses in an autoregressive manner between the current and target
state of the character. In addition, to satisfy poses which are manually
modified by the animators or where certain end effectors serve as constraints
to be reached by the animation, a learned bi-directional control scheme is
implemented to satisfy such constraints. The results demonstrate that using
phases for motion in-betweening tasks sharpen the interpolated movements, and
furthermore stabilizes the learning process. Moreover, using phases for motion
in-betweening tasks can also synthesize more challenging movements beyond
locomotion behaviors. Additionally, style control is enabled between given
target keyframes. Our proposed framework can compete with popular
state-of-the-art methods for motion in-betweening in terms of motion quality
and generalization, especially in the existence of long transition durations.
Our framework contributes to faster prototyping workflows for creating animated
character sequences, which is of enormous interest for the game and film
industry.
