使用opencv转视频格式

因为需要把NV21的1080p视频转成YV12，又不知道用什么工具，所以直接写了代码

可能代码有点问题，不过能实现我的要求，但还是希望各位大手子在留言区点评下。

这是Ubuntu系统下的代码，可能在windows上有所不同。因为懒得弄输入法，所以当时写的是英文的注释，见谅

#include 
#include 
#include 
#include 
#include 

#include 
#include 
#include 
#include 

using namespace std;
using namespace cv;

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    // 1080p
    uint64_t lenth = 1080 * 1920 * 3 / 2;
    string read_file_name = "/newSpace/200_1080p.nv21";
    ifstream ifs(read_file_name);
    FILE *save_file;
    save_file = fopen("/newSpace/result.YUV", "ab+");
    // 获取文件大小
    ifs.seekg(0, ifs.end);
    uint64_t src_size = static_cast(ifs.tellg());
    ifs.seekg(0, ifs.beg);  //一定要把它移回开头
    // max index of the file
    uint64_t max_index = src_size / lenth;
    uint8_t *result = new uint8_t[lenth];
    // loop
    for (uint64_t index = 0; index < max_index; index++) {
        uint8_t *p = new uint8_t[lenth];
        uint8_t *head = p;
        uint8_t c;
        uint64_t count = lenth * index;
        // get bytes from file
        while (count < lenth * (index + 1) ) {
            c = static_cast(ifs.get());
                count++;
                if (count < lenth * index) {
                    continue;
                }
                *p = c;
                p++;
       }
        // convert I420 to YV12
        Mat pic1(1080 * 3 / 2, 1920, CV_8UC1, head);
        Mat pic2(1080, 1920, CV_8UC3);
        Mat pic3;
        cvtColor(pic1, pic2, CV_YUV2BGRA_NV21);
        cvtColor(pic2, pic3, CV_BGRA2YUV_YV12);
        // 这个是为了deubg
        // imwrite("/newSpace/" + to_string(index) + "-0.jpg", pic1);
        // imwrite("/newSpace/" + to_string(index) + "-1.jpg", pic2);
        // imwrite("/newSpace/" + to_string(index) + "-2.jpg", pic3);
        // copy the picture to result
        ::memcpy(result, pic3.data, lenth);
//        delete[] p;
        // save
        fwrite(result, 1, lenth, save_file);
    }




    return a.exec();
}