  Despite significant efforts, cutting-edge video segmentation methods still
remain sensitive to occlusion and rapid movement, due to their reliance on the
appearance of objects in the form of object embeddings, which are vulnerable to
these disturbances. A common solution is to use optical flow to provide motion
information, but essentially it only considers pixel-level motion, which still
relies on appearance similarity and hence is often inaccurate under occlusion
and fast movement. In this work, we study the instance-level motion and present
InstMove, which stands for Instance Motion for Object-centric Video
Segmentation. In comparison to pixel-wise motion, InstMove mainly relies on
instance-level motion information that is free from image feature embeddings,
and features physical interpretations, making it more accurate and robust
toward occlusion and fast-moving objects. To better fit in with the video
segmentation tasks, InstMove uses instance masks to model the physical presence
of an object and learns the dynamic model through a memory network to predict
its position and shape in the next frame. With only a few lines of code,
InstMove can be integrated into current SOTA methods for three different video
segmentation tasks and boost their performance. Specifically, we improve the
previous arts by 1.5 AP on OVIS dataset, which features heavy occlusions, and
4.9 AP on YouTubeVIS-Long dataset, which mainly contains fast-moving objects.
These results suggest that instance-level motion is robust and accurate, and
hence serving as a powerful solution in complex scenarios for object-centric
video segmentation.
