# Learning Neural Volumetric Representations of Dynamic Humans in Minutes

## TL;DR

This paper introduces a fast method for reconstructing dynamic human scenes as neural volumetric videos from sparse multi-view videos, achieving similar quality to slower methods in just minutes.

## Contribution

A novel part-based voxelized human representation and 2D motion parameterization scheme enable rapid learning of neural volumetric videos from sparse views.

## Key findings

- Training time reduced to about 5 minutes on a single GPU.
- Achieves competitive visual quality with prior methods.
- Model is 100 times faster than traditional per-scene optimization.

## Abstract

This paper addresses the challenge of quickly reconstructing free-viewpoint videos of dynamic humans from sparse multi-view videos. Some recent works represent the dynamic human as a canonical neural radiance field (NeRF) and a motion field, which are learned from videos through differentiable rendering. But the per-scene optimization generally requires hours. Other generalizable NeRF models leverage learned prior from datasets and reduce the optimization time by only finetuning on new scenes at the cost of visual fidelity. In this paper, we propose a novel method for learning neural volumetric videos of dynamic humans from sparse view videos in minutes with competitive visual quality. Specifically, we define a novel part-based voxelized human representation to better distribute the representational power of the network to different human parts. Furthermore, we propose a novel 2D motion parameterization scheme to increase the convergence rate of deformation field learning. Experiments demonstrate that our model can be learned 100 times faster than prior per-scene optimization methods while being competitive in the rendering quality. Training our model on a $512 \times 512$ video with 100 frames typically takes about 5 minutes on a single RTX 3090 GPU. The code will be released on our project page: https://zju3dv.github.io/instant_nvr