Function CMSyncGetRelativeRate 

pub unsafe extern "C-unwind" fn CMSyncGetRelativeRate(
    of_clock_or_timebase: &CMClockOrTimebase,
    relative_to_clock_or_timebase: &CMClockOrTimebase,
) -> f64

Available on crate feature CMSync only.

Queries the relative rate of one timebase or clock relative to another timebase or clock.

If both have a common source, this calculation is performed purely based on the rates in the common tree rooted in that source. If they have different source clocks (or are both clocks), this calculation takes into account the measured drift between the two clocks, using host time as a pivot. The rate of a moving timebase relative to a stopped timebase is a NaN. Calling CMTimebaseGetEffectiveRate(timebase) is equivalent to calling CMClockRef clock = CMTimebaseCopyUltimateSourceClock(timebase); CMSyncGetRelativeRate(timebase, clock). CFRelease(clock);

Safety

• of_clock_or_timebase should be of the correct type.
• relative_to_clock_or_timebase should be of the correct type.