Membrane.Time.vm_time

You're seeing just the function vm_time, go back to Membrane.Time module for more information.

Specs

vm_time() :: t()

Returns current Erlang VM system time based on System.system_time/0 in Membrane.Time units.

It is the VM view of the os_time/0. They may not match in case of time warps. It is not monotonic.