# Wireless Software Synchronization of Multiple Distributed Cameras

## TL;DR

This paper introduces a software-based method for precisely synchronizing multiple smartphones over WiFi for multi-camera imaging, achieving microsecond accuracy without special hardware.

## Contribution

It presents a novel two-stage algorithm for clock synchronization and image alignment across multiple commodity smartphones, enabling improved multi-view applications.

## Key findings

- Achieves less than 250 microseconds synchronization accuracy.
- Validates effectiveness with multi-camera rig experiments.
- Enhances multi-view stereo and scene stitching quality.

## Abstract

We present a method for precisely time-synchronizing the capture of image sequences from a collection of smartphone cameras connected over WiFi. Our method is entirely software-based, has only modest hardware requirements, and achieves an accuracy of less than 250 microseconds on unmodified commodity hardware. It does not use image content and synchronizes cameras prior to capture. The algorithm operates in two stages. In the first stage, we designate one device as the leader and synchronize each client device's clock to it by estimating network delay. Once clocks are synchronized, the second stage initiates continuous image streaming, estimates the relative phase of image timestamps between each client and the leader, and shifts the streams into alignment. We quantitatively validate our results on a multi-camera rig imaging a high-precision LED array and qualitatively demonstrate significant improvements to multi-view stereo depth estimation and stitching of dynamic scenes. We release as open source 'libsoftwaresync', an Android implementation of our system, to inspire new types of collective capture applications.