Hong, SeokhyeonKim, HaeminCho, KyungminNoh, JunyongSkouras, MelinaWang, He2024-08-202024-08-2020241467-8659https://doi.org/10.1111/cgf.15171https://diglib.eg.org/handle/10.1111/cgf15171Motion in-betweening has emerged as a promising approach to enhance the efficiency of motion creation due to its flexibility and time performance. However, previous in-betweening methods are limited to generating short transitions due to growing pose ambiguity when the number of missing frames increases. This length-related constraint makes the optimization hard and it further causes another constraint on the target pose, limiting the degrees of freedom for artists to use. In this paper, we introduce a keyframe-driven approach that effectively solves the pose ambiguity problem, allowing robust in-betweening performance on various lengths of missing frames. To incorporate keyframe-driven motion synthesis, we introduce a keyframe score that measures the likelihood of a frame being used as a keyframe as well as an adaptive keyframe selection method that maintains appropriate temporal distances between resulting keyframes. Additionally, we employ phase manifolds to further resolve the pose ambiguity and incorporate trajectory conditions to guide the approximate movement of the character. Comprehensive evaluations, encompassing both quantitative and qualitative analyses, were conducted to compare our method with state-of-theart in-betweening approaches across various transition lengths. The code for the paper is available at https://github. com/seokhyeonhong/long-mibCCS Concepts: Computing methodologies → AnimationComputing methodologies → Animation10.1111/cgf.1517112 pages