  Looping videos are short video clips that can be looped endlessly without
visible seams or artifacts. They provide a very attractive way to capture the
dynamism of natural scenes. Existing methods have been mostly limited to 2D
representations. In this paper, we take a step forward and propose a practical
solution that enables an immersive experience on dynamic 3D looping scenes. The
key challenge is to consider the per-view looping conditions from asynchronous
input while maintaining view consistency for the 3D representation. We propose
a novel sparse 3D video representation, namely Multi-Tile Video (MTV), which
not only provides a view-consistent prior, but also greatly reduces memory
usage, making the optimization of a 4D volume tractable. Then, we introduce a
two-stage pipeline to construct the 3D looping MTV from completely asynchronous
multi-view videos with no time overlap. A novel looping loss based on video
temporal retargeting algorithms is adopted during the optimization to loop the
3D scene. Experiments of our framework have shown promise in successfully
generating and rendering photorealistic 3D looping videos in real time even on
mobile devices. The code, dataset, and live demos are available in
https://limacv.github.io/VideoLoop3D_web/.
