  Video conferencing has caught much more attention recently. High fidelity and
low bandwidth are two major objectives of video compression for video
conferencing applications. Most pioneering methods rely on classic video
compression codec without high-level feature embedding and thus can not reach
the extremely low bandwidth. Recent works instead employ model-based neural
compression to acquire ultra-low bitrates using sparse representations of each
frame such as facial landmark information, while these approaches can not
maintain high fidelity due to 2D image-based warping. In this paper, we propose
a novel low bandwidth neural compression approach for high-fidelity portrait
video conferencing using implicit radiance fields to achieve both major
objectives. We leverage dynamic neural radiance fields to reconstruct
high-fidelity talking head with expression features, which are represented as
frame substitution for transmission. The overall system employs deep model to
encode expression features at the sender and reconstruct portrait at the
receiver with volume rendering as decoder for ultra-low bandwidth. In
particular, with the characteristic of neural radiance fields based model, our
compression approach is resolution-agnostic, which means that the low bandwidth
achieved by our approach is independent of video resolution, while maintaining
fidelity for higher resolution reconstruction. Experimental results demonstrate
that our novel framework can (1) construct ultra-low bandwidth video
conferencing, (2) maintain high fidelity portrait and (3) have better
performance on high-resolution video compression than previous works.
