NV21转YUV420P的代码，测试通过

public final static int NV21_TO_yuv420P(byte[] dst, byte[] src, int w, int h)
    {
        int ysize = w * h;
        int usize = w * h * 1 / 4;
        byte[] dsttmp = dst;
        // y
        System.arraycopy(src, 0, dst, 0, ysize);
        // u, 1/4
        int srcPointer = ysize;
        int dstPointer = ysize;
        int count = usize;
        while (count > 0)
        {
            srcPointer++;
            dst[dstPointer] = src[srcPointer];
            dstPointer++;
            srcPointer++;
            count--;
        }
        // v, 1/4
        srcPointer = ysize;
        count = usize;
        while (count > 0)
        {
            dst[dstPointer] = src[srcPointer];
            dstPointer++;
            srcPointer += 2;
            count--;
        }
        dst = dsttmp;
        // _EF_TIME_DEBUG_END(0x000414141);
        return 0;
    }