What's the function of variables "nu" and "nv" in method saveYuvDataToJPEG?

[mizhoux]

byte[] y = new byte[width * height];
byte[] u = new byte[width * height / 4];
byte[] v = new byte[width * height / 4];
byte[] nu = new byte[width * height / 4]; //
byte[] nv = new byte[width * height / 4];

System.arraycopy(yuvFrame, 0, y, 0, y.length);
for (int i = 0; i < u.length; i++) {
      v[i] = yuvFrame[y.length + 2 * i];
      u[i] = yuvFrame[y.length + 2 * i + 1];
}

The code above seems that the YUV data received from the UVA is already encoded by NV21, the array u and array v represent the data U and V respectively. So I'm confused about the function of the following code due to I don't know what the variables "nu" and "nv" are for.

int uvWidth = width / 2;
int uvHeight = height / 2;
for (int j = 0; j < uvWidth / 2; j++) {
    for (int i = 0; i < uvHeight / 2; i++) {
        byte uSample1 = u[i * uvWidth + j];
        byte uSample2 = u[i * uvWidth + j + uvWidth / 2];
        byte vSample1 = v[(i + uvHeight / 2) * uvWidth + j];
        byte vSample2 = v[(i + uvHeight / 2) * uvWidth + j + uvWidth / 2];
        nu[2 * (i * uvWidth + j)] = uSample1;
        nu[2 * (i * uvWidth + j) + 1] = uSample1;
        nu[2 * (i * uvWidth + j) + uvWidth] = uSample2;
        nu[2 * (i * uvWidth + j) + 1 + uvWidth] = uSample2;
        nv[2 * (i * uvWidth + j)] = vSample1;
        nv[2 * (i * uvWidth + j) + 1] = vSample1;
        nv[2 * (i * uvWidth + j) + uvWidth] = vSample2;
        nv[2 * (i * uvWidth + j) + 1 + uvWidth] = vSample2;
    }
}

//nv21test
byte[] bytes = new byte[yuvFrame.length];
System.arraycopy(y, 0, bytes, 0, y.length);
for (int i = 0; i < u.length; i++) {
    bytes[y.length + (i * 2)] = nv[i];
    bytes[y.length + (i * 2) + 1] = nu[i];
}

[neilyoung]

did you ever get an answer somehow?