NV12轉YUV420P

         在用MediaCodec編碼的時候，如果設置顏色空間爲YUV420SP，那麼則需要轉換一下，

         NV21 顏色空間排列 ：YYYYYYYY VUVU

         YUV420SP顏色排列順序爲：YYYYYYY UVUV

  YUV420 是與NV12對應的，但是5.0一下的安卓手機支持這個預覽顏色的不多，則需要將VU順序進行轉換，具體算法如下：

void BGR2NV21( unsigned char *imgSrc, unsigned char *imgDst, int width, int height )
{
	int w, h;
	int shift = 14, offset1 = 8192, offset2 = 2105344;
	int C0 = 1868, C1 = 9617, C2 = 4899, C3 = 11682, C4 = 9241;

	int r1,r2,g1,g2,b1,b2;
	
	unsigned char * pRGB1 = imgSrc;
	unsigned char * pRGB2 = imgSrc+width*3;

	unsigned char * pDY1 = imgDst;
	unsigned char * pDY2 = imgDst+width;
	unsigned char * pDUV = imgDst+width*height;

	for ( h = 0; h < height; h += 2 )
	{
		for ( w = 0; w < width; w += 2 )
		{
			b1 = *pRGB1++;
			g1 = *pRGB1++;
			r1 = *pRGB1++;
			*pDY1  = (b1 * C0 + g1 * C1 + r1 * C2 + offset1) >> shift;
			*pDUV++ = ((r1 - *pDY1) * C3 + offset2) >> shift;
			*pDUV++ = ((b1 - *pDY1) * C4 + offset2) >> shift;
			pDY1++;

			b1 = *pRGB1++;
			g1 = *pRGB1++;
			r1 = *pRGB1++;
			*pDY1  = (b1 * C0 + g1 * C1 + r1 * C2 + offset1) >> shift;
			pDY1++;

			b2 = *pRGB2++;
			g2 = *pRGB2++;
			r2 = *pRGB2++;
			*pDY2  = (b2 * C0 + g2 * C1 + r2 * C2 + offset1) >> shift;
			pDY2++;

			b2 = *pRGB2++;
			g2 = *pRGB2++;
			r2 = *pRGB2++;
			*pDY2  = (b2 * C0 + g2 * C1 + r2 * C2 + offset1) >> shift;
			pDY2++;
		}
		pRGB1 += 3*width;
		pRGB2 += 3*width;
		pDY1 += width;
		pDY2 += width;

	}
}
#define MAX(a ,b) ((a > b) ? a : b)
#define MIN(a ,b) ((a < b) ? a : b)
#define CLAP(a) (MAX((MIN(a, 0xff)), 0x00)) 
void NV212BGR( unsigned char *imgY, unsigned char *imgDst,int width, int height )
{
	int w, h;
	int shift = 14, offset = 8192;
	int C0 = 22987, C1 = -11698, C2 = -5636, C3 = 29049;

	int y1,y2,u1,v1;

	unsigned char * pY1 = imgY;
	unsigned char * pY2 = imgY+width;
	unsigned char * pUV = imgY+width*height;
	
	unsigned char * pD1 = imgDst;
	unsigned char * pD2 = imgDst+width*3;

	for ( h = 0; h < height; h +=2 )
	{
		for ( w = 0; w < width; w +=2 )
		{
			v1 = *pUV-128;
			pUV++;
			u1 = *pUV-128;
			pUV++;

			
			y1 = *pY1;
			y2 = *pY2;

			*pD1++ = CLAP(y1+((u1 * C3 + offset) >> shift));
			*pD1++ = CLAP(y1+((u1 * C2 + v1 * C1 + offset) >> shift));
			*pD1++ = CLAP(y1+((v1 * C0 + offset) >> shift));
			*pD2++ = CLAP(y2+((u1 * C3 + offset) >> shift));
			*pD2++ = CLAP(y2+((u1 * C2 + v1 * C1 + offset) >> shift));
			*pD2++ = CLAP(y2+((v1 * C0 + offset) >> shift));

			pY1++;
			pY2++;
			y1 = *pY1;
			y2 = *pY2;

			*pD1++ = CLAP(y1+((u1 * C3 + offset) >> shift));
			*pD1++ = CLAP(y1+((u1 * C2 + v1 * C1 + offset) >> shift));
			*pD1++ = CLAP(y1+((v1 * C0 + offset) >> shift));
			*pD2++ = CLAP(y2+((u1 * C3 + offset) >> shift));
			*pD2++ = CLAP(y2+((u1 * C2 + v1 * C1 + offset) >> shift));
			*pD2++ = CLAP(y2+((v1 * C0 + offset) >> shift));
			pY1++;
			pY2++;

		}
		pY1 += width;
		pY2 += width;
		pD1 += 3*width;
		pD2 += 3*width;

	}
}