This ioctl call returns the current value of the system time counter
(which is driven by a PES filter of type
Some hardware supports more than one STC, so you must specify which one by
num field of stc before the ioctl (range 0...n).
The result is returned in form of a ratio with a 64 bit numerator
and a 32 bit denominator, so the real 90kHz STC value is
stc->stc / stc->base.