マイポータル
https://qiita.com/carpenders/items/adb743f0a308f6786c73
sv3c.cpp
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct pack_ {
        char code[4];
        int len;
        int magic1;
        int magic2;
};

static void dump(struct pack_ &pack)
{
        char code[5];
        memcpy(code,pack.code,sizeof(pack.code));
        code[4] = 0;
        printf("code [%s] len %d(0x%x) magic1 0x%x magic2 0x%x\n",
                code,pack.len,pack.len,pack.magic1,pack.magic2);
}

int main(int argc,char *argv[])
{
        FILE *ifp,*ofp;
        ifp = fopen(argv[1],"rb");
        char ofname[4096];
        sprintf(ofname,"%s.264",argv[1]);
        ofp = fopen(ofname,"wb");
        if(ifp != NULL && ofp != NULL){
                struct pack_ pack;
                int size = sizeof(pack);
                int rd,wr;
                bool ok = true;
                if(ok){
                        rd = fread(&pack,1,size,ifp);
                        ok = rd == size;
                        if(ok){
                                dump(pack);
                        }
                        while(ok){
                                if(ok){
                                        rd = fread(&pack,1,size,ifp);
                                        ok = rd == size;
                                        if(ok){
                                                dump(pack);
                                        }
                                }
                                if(ok){
                                        void *buf;
                                        buf = malloc(pack.len);
                                        rd = fread(buf,1,pack.len,ifp);
                                        ok = rd == pack.len;
                                        if(ok){
                                                wr = fwrite(buf,1,rd,ofp);
                                                ok = wr == rd;
                                        }
                                        free(buf);
                                }
                        }
                }
                if(ifp != NULL){
                        fclose(ifp);
                }
                if(ofp != NULL){
                        fclose(ofp);
                }
        }
        return 0;
}
参考
https://oxynotes.com/?p=11912