Function convert_into 

pub fn convert_into(
    pixels: &[u8],
    stride: usize,
    width: usize,
    height: usize,
    rgba: bool,
    i444: bool,
    full_range: bool,
    bt601: bool,
    threads: usize,
    y: &mut [u8],
    u: &mut [u8],
    v: &mut [u8],
    strides: (usize, usize),
) -> Result<(), String>

Convert a packed host frame into planes a library owns, at strides (luma, chroma) bytes per row, as Planes::convert does into its own.