Not only to VDI but also using the same VBOXmanage tools of VirtualBox the user can convert the ISO image file to VDMK or VHD.
Yes, this is the method in which we directly convert the ISO image file (.iso) into VDI (virtual disk image) format using VirtualBox. Although you can use directly the ISO file to boot any OS on VirtualBox, HyperV or VMware Workstations, however, in case you don’t want to first boot & install ISO file to convert it to VDI or VDMK (virtual hard drives) format. The ISO file is a widely used Disk file format for installing different bootable operating systems.