NV12转换为I420

int nv12Toi420(int nWidth,int nHeight,int nPitch,CUdeviceptr* Src_NV12,unsigned char *Dst_i420)
{
	if(m_pTempBufSize < nPitch * nHeight * 3 / 2)
	{
		m_pTempBufSize = nPitch * nHeight * 3 / 2;
		if(m_pBuf)
		{
			free(m_pBuf);
			m_pBuf = (unsigned char* )malloc(m_pTempBufSize);
		}
		else
			m_pBuf = (unsigned char* )malloc(m_pTempBufSize);
	}
	
	memcpy(m_pBuf, Src_NV12, nPitch * nHeight * 3 / 2);
	int dst_pos = 0;
	int src_pos = 0;

	for (int i = 0;i<nHeight*3/2;i++)
	{
		memcpy(Dst_i420+dst_pos, m_pBuf+src_pos, nWidth);
		dst_pos += nWidth;
		src_pos += nPitch;

	}

	int i = 0;
	// Write Cb
	for(int idx = 0; idx <  (nWidth*nHeight/2); idx+=2)
	{
		memcpy(m_pUV[0] + i, Dst_i420+nWidth*nHeight + idx,1);
		i++;
	}
	i =0;
	// Write Cr
	for(int idx = 1; idx <  (nWidth*nHeight/2); idx+=2)
	{
		memcpy(m_pUV[1]+i,Dst_i420+nWidth*nHeight+idx,1);
		i++;
	}

	memcpy(Dst_i420 + nWidth*nHeight, m_pUV[0],nWidth*nHeight/4);
	memcpy(Dst_i420+nWidth*nHeight + nWidth*nHeight/4, m_pUV[1], nWidth*nHeight/4);

	return 1;

}