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/.

翻译：循环视频是指能够无缝无限循环播放且无明显接缝或伪影的短视频片段，它们为捕捉自然场景的动态性提供了一种极具吸引力的方式。现有方法大多局限于二维表示。本文向前迈出一步，提出了一种实用解决方案，可实现动态三维循环场景的沉浸式体验。关键挑战在于：在保持三维表示的视角一致性的同时，考虑异步输入下的逐视角循环条件。我们提出了一种新颖的稀疏三维视频表示——多图块视频（MTV），它不仅提供了视角一致先验，还大幅降低了内存占用，使四维体积的优化变得可行。接着，我们引入了一个两阶段流水线，从完全异步（无时间重叠）的多视角视频中构建三维循环MTV。在优化过程中，我们采用了一种基于视频时间重定向算法的新型循环损失函数来实现三维场景的循环。实验表明，我们的框架能够成功生成并实时渲染逼真的三维循环视频，甚至在移动设备上亦可实现。代码、数据集及在线演示请访问 https://limacv.github.io/VideoLoop3D_web/。