ColorConversions.java

public static byte[] NV21toYUV420Planar(byte[] input, byte[] output, int width, int height) {
    final int frameSize = width * height;
    final int qFrameSize = frameSize/4;

    System.arraycopy(input, 0, output, 0, frameSize); // Y

    byte v, u;

    for (int i = 0; i < qFrameSize; i++) {
        v = input[frameSize + i*2];
        u = input[frameSize + i*2 + 1];

        output[frameSize + i + qFrameSize] = v;
        output[frameSize + i] = u;
    }

    return output;
}

public static byte[] NV21toYUV420SemiPlanar(byte[] input, byte[] output, int width, int height) {
    final int frameSize = width * height;
    final int qFrameSize = frameSize/4;

    System.arraycopy(input, 0, output, 0, frameSize); // Y

    byte v, u;

    for (int i = 0; i < qFrameSize; i++) {
        v = input[frameSize + i*2];
        u = input[frameSize + i*2 + 1];

        output[frameSize + i*2] = u;
        output[frameSize + i*2 + 1] = v;
    }

    return output;
}