Convert YUV NV21 to I420

YUV_NV21toI420.java

    /** Convert NV21 (YYYYYYYYY:VUVU) to I420 (YYYYYYYY:UU:VV)  
    Convert I420 (YYYYYYYY:UU:VV) to NV21 (YYYYYYYYY:VUVU) can be get here: https://gist.github.com/pnemonic78/2d8411ed6b0bd6c71b651800bc97eb8e
    */
    public byte[] NV21toI420(final byte[] input, byte[] output, final int width, final int height) {
        if (output == null) {
            output = new byte[input.length];
        }
        final int size = width * height;
        final int quarter = size / 4;
        final int v0 = size + quarter;

        System.arraycopy(input, 0, output, 0, size); // Y is same

        for (int u = size, v = v0, o = size; u < v0; u++, v++, o += 2) {
            output[v] = input[o]; // For NV21, V first
            output[u] = input[o + 1]; // For NV21, U second
        }
        return output;
    }