Virtual Disk Image .vdi files can be for example exported to Parallels images (.hdd) with the multi-platform VirtualBox virtualization software currently developed by Oracle.
Open VirtualBox and make a few steps:
- Click on File menu ► Virtual Media Manager.
- Select virtual hard drive that you need to convert to HDD ► Click on Copy option in upper menu.
- Click on Next button ► Set Virtual disk file type to HDD.
- Select storage details, new location, Click on Copy button and wait until the conversion is finished.
Alternative would be to do this conversion with Parallels Workstation as it should accept .vdi files from VirtualBox just fine.