rgb转yuv420

bool  RGB2YUV420(LPBYTE RgbBuf,UINT nWidth,UINT nHeight,LPBYTE yuvBuf,unsigned long *len)
{

    int i, j;
 unsigned char*bufY, *bufU, *bufV, *bufRGB,*bufYuv;
 memset(yuvBuf,0,(unsigned int )*len);
 bufY = yuvBuf;
 bufV = yuvBuf + nWidth * nHeight;
 bufU = bufV + (nWidth * nHeight* 1/4);
 *len = 0; 
 unsigned char y, u, v, r, g, b,testu,testv;
    unsigned int ylen = nWidth * nHeight;
 unsigned int ulen = (nWidth * nHeight)/4;
 unsigned int vlen = (nWidth * nHeight)/4; 
 for (j = 0; j<nHeight;j++)
 {
  bufRGB = RgbBuf + nWidth * (nHeight - 1 - j) * 3 ;
  for (i = 0;i<nWidth;i++)
  {
   int pos = nWidth * i + j;
   r = *(bufRGB++);
   g = *(bufRGB++);
   b = *(bufRGB++);

  y = (unsigned char)( ( 66 * r + 129 * g +  25 * b + 128) >> 8) + 16  ;          
     u = (unsigned char)( ( -38 * r -  74 * g + 112 * b + 128) >> 8) + 128 ;          
        v = (unsigned char)( ( 112 * r -  94 * g -  18 * b + 128) >> 8) + 128 ;
  *(bufY++) = max( 0, min(y, 255 ));
   
   if (j%2==0&&i%2 ==0)
   {
    if (u>255)
    {
     u=255;
    }
    if (u<0)
    {
     u = 0;
    }
    *(bufU++) =u;
//存u分量
   }
   else
   {
    //存v分量
    if (i%2==0)
    {
     if (v>255)
     {
      v = 255;
     }
     if (v<0)
     {
      v = 0;
     }
     *(bufV++) =v;
    
    }
   }

  }

 }
 *len = nWidth * nHeight+(nWidth * nHeight)/2;
 return true;
}