yv12、I420、nv12、nv21区别及相互转换方法

YUV420P，Y，U，V三个分量都是平面格式，分为I420和YV12。I420格式和YV12格式的不同处在U平面和V平面的位置不同。在I420格式中，U平面紧跟在Y平面之后，然后才是V平面（即：YUV）；但YV12则是相反（即：YVU）。
YUV420SP, Y分量平面格式，UV打包格式, 即NV12。 NV12与NV21类似，U 和 V 交错排列,不同在于UV顺序。
I420: YYYYYYYY UU VV    =>YUV420P
YV12: YYYYYYYY VV UU    =>YUV420P
NV12: YYYYYYYY UVUV     =>YUV420SP
NV21: YYYYYYYY VUVU     =>YUV420SP
1、NV21转nv12
private void swapNV21ToNV12(byte[] nv21,byte[] nv12,int width,int height){
if(nv21 == null || nv12 == null)return;
int framesize = width*height;
int i = 0,j = 0;
System.arraycopy(nv21, 0, nv12, 0, framesize);
for (j = 0; j < framesize/2; j+=2)
{
nv12[framesize + j + 1] = nv21[j + framesize];
}

for (j = 0; j < framesize/2; j += 2)
{
nv12[framesize + j] = nv21[j + framesize + 1];
}
}

2、YV12转I420
private void swapYV12toI420(byte[] yv12bytes, byte[] i420bytes, int width, int height)
{
System.arraycopy(yv12bytes, 0, i420bytes, 0,width*height);
System.arraycopy(yv12bytes, width*height+width*height/4, i420bytes, width*height,width*height/4);
System.arraycopy(yv12bytes, width*height, i420bytes, width*height+width*height/4,width*height/4);
}

3、yv12转nv12
void swapYV12toNV12(byte[] yv12bytes, byte[] nv12bytes, int width,int height)
{
int nLenY = width * height;
int nLenU = nLenY / 4;

System.arraycopy(yv12bytes, 0, nv12bytes, 0, width * height);
for (int i = 0; i < nLenU; i++) {
nv12bytes[nLenY + 2 * i + 1] = yv12bytes[nLenY + i];
nv12bytes[nLenY + 2 * i] = yv12bytes[nLenY + nLenU + i];
}
}

4、nv12转I420
void swapNV12toI420(byte[] nv12bytes, byte[] i420bytes, int width,int height)
{
int nLenY = width * height;
int nLenU = nLenY / 4;

System.arraycopy(nv12bytes, 0, i420bytes, 0, width * height);
for (int i = 0; i < nLenU; i++) {
i420bytes[nLenY + i] = nv12bytes[nLenY + 2 * i + 1];
i420bytes[nLenY + nLenU + i] = nv12bytes[nLenY + 2 * i];
}