public void set_start_time
Set the start time of an element.
The start time of the element is the running time of the element when it last went to the PAUSED state. In READY or after a flushing seek, it
is set to 0.
Toplevel elements like Pipeline will manage the start_time and base_time on its
children. Setting the start_time to CLOCK_TIME_NONE on such a toplevel
element will disable the distribution of the base_time to the children and can be useful if the application manages the base_time itself, for
example if you want to synchronize capture from multiple pipelines, and you can also ensure that the pipelines have the same clock.
||the base time to set.