Function convert_to_nv12_mt 

pub(crate) fn convert_to_nv12_mt(
    src: &[u8],
    src_stride: u32,
    width: usize,
    height: usize,
    rgba_input: bool,
    y_buf: &mut [u8],
    uv_buf: &mut [u8],
    strides: (usize, usize),
    bands: usize,
) -> Result<(), YuvError>

Convert a packed buffer, B,G,R,A or with rgba_input R,G,B,A, to 8-bit 4:2:0 BT.709 limited range as NV12, a luma plane and an interleaved chroma one strides bytes a row, the picture x264 encodes in place (Nv12Planes), in the bands convert_to_yuv_mt splits it into. Its samples are the ones convert_to_yuv_mt writes to I420, the chroma interleaved.