Function getVapourSynthAPI 

pub unsafe extern "system-unwind" fn getVapourSynthAPI(
    version: c_int,
) -> *const VSAPI

Returns a pointer to the global VSAPI instance.

Returns NULL if the requested API version is not supported or if the system does not meet the minimum requirements to run VapourSynth. It is recommended to pass VAPOURSYNTH_API_VERSION