YUV格式学习：NV12和YUV420P格式互换

NV12和YUV420的转换是在相同采样空间的转换，只是个别分量位置的调整，只要明白了Y、U、V分量的布置，就很容易写出来。

代码如下：

/**
yyyy yyyy
uv    uv
->
yyyy yyyy
uu
vv
*/
void yuv420sp_to_yuv420p(unsigned char* yuv420sp, unsigned char* yuv420p, int width, int height)
{
int i, j;
int y_size = width * height;

unsigned char* y = yuv420sp;
unsigned char* uv = yuv420sp + y_size;

unsigned char* y_tmp = yuv420p;
unsigned char* u_tmp = yuv420p + y_size;
unsigned char* v_tmp = yuv420p + y_size * 5 / 4;

// y
memcpy(y_tmp, y, y_size);

// u
for (j = 0, i = 0; j < y_size/2; j+=2, i++)
{
u_tmp[i] = uv[j];
v_tmp[i] = uv[j+1];
}
}

/**
yyyy yyyy
uu
vv
->
yyyy yyyy
uv    uv
*/
void yuv420p_to_yuv420sp(unsigned char* yuv420p, unsigned char* yuv420sp, int width, int height)
{
int i, j;
int y_size = width * height;

unsigned char* y = yuv420p;
unsigned char* u = yuv420p + y_size;
unsigned char* v = yuv420p + y_size * 5 / 4;

unsigned char* y_tmp = yuv420sp;
unsigned char* uv_tmp = yuv420sp + y_size;

// y
memcpy(y_tmp, y, y_size);

// u
for (j = 0, i = 0; j < y_size/2; j+=2, i++)
{
// 此处可调整U、V的位置，变成NV12或NV21
#if 01
uv_tmp[j] = u[i];
uv_tmp[j+1] = v[i];
#else
uv_tmp[j] = v[i];
uv_tmp[j+1] = u[i];
#endif
}
}

后记：

一口气把自己研究很久的东西写出来，好像都没写到点子上。以前也尝试过写技术性很强的文章，到处找资料，找出处，但后来发觉自己不是那块料，于是就直接贴代码，理论的东西反而不说——因为说不清，也怕说错。

关于YUV，初步听说是在6、7年前的大学，开始接触是在4、5年前，而真正了解其原理，却是近些年。学习进度不可谓不慢。写出来，也算有个交待。也为自己准备实现的YUV播放器做些准备。

迟 2015.8.5 晚上