US Patent 10353424 Clock synchronisation

A first device for playing media synchronously with a second device, includes a hardware clock having an adjustable clock frequency; a software clock configured to derive time in dependence on the hardware clock; a controller configured to: determine a synchronization error between the software clock and a clock of the second device; and adjust the clock frequency of the hardware clock in dependence on the synchronization error; and a media playout device for playing media and configured to be clocked by the hardware clock.