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;
}