return 0;
return url_ftell(bc) - 8;
static int find_startcode(ByteIOContext *bc, uint64_t code, int64_t pos){    for(;;){        uint64_t startcode= find_any_startcode(bc, pos);        if(startcode == code)            return 0;        else if(startcode == 0)            return -1;        pos=-1;    }}