Abstract: We present a novel constraint-based keyframe extraction technique, Key Probe. Based on animator-specified constraints, the method converts a skeleton-based motion or animated mesh to a keyframe-based representation. In contrast to previous curve simplification or clustering methods, we cast the keyframe extraction problem as a constrained matrix factorization problem and solve the problem based on the least-squares optimization technique. The extracted keyframes have two uses: they could be used for browsing or they may be blended to reconstruct all other frames of an animation. Our approach is general and suitable for both rigid-body and soft-body animations. Experiments on various types of animation examples show that the proposed method produces remarkable results in terms of quality and compression ratio. Empirical tests also show that our algorithm consistently offers better efficiency than those by principal component analysis (PCA) and independent component analysis (ICA).