Check out our new work on sensor synchronization with IMU data, here.
We have also released the mobile application of this method to synchronize multiple smartphones: https://github.com/MobileRoboticsSkoltech/twist-n-sync
Experiment setting where two mobiles capture with microsecond accuracy the instant of time of the snow hitting a solid surface
An example of an application after the synchronization of two smartphones Samsung S10 and phase sync. of the cameras.