Function scale 

pub unsafe fn scale(
    _ctx: *mut SwsContext,
    _src: *const *const u8,
    _src_stride: *const c_int,
    _src_slice_y: c_int,
    _src_slice_h: c_int,
    _dst: *const *mut u8,
    _dst_stride: *const c_int,
) -> Result<c_int, c_int>