Is there a way to convert a VDI HDD to a VHD?
There is a new option now in VirtualBox 4.1 to copy a VDI with a new format (including VHD), which is equivalent to the command Derek P pointed out last year, but in a nice GUI.
- Open Virtual Box and select Files > Virtual Media Manager.
- Select an existing disk file on the Hard Disks tab and click the Copy button.
- Complete the steps in the wizard. Select VHD when prompted for the file type.
Yes, as Derek said, builtin tool with VirtualBox works well under Windows OS without any third party software. Converted OS is booting without any troubles, for more information with example steps check this post,
Without downloading and installing VirtualBox, you can use qemu-img from QEMU package:
qemu-img.exe convert source.img -O vhdx -o subformat=dynamic dest.vhdx
Download for windows: https://cloudbase.it/qemu-img-windows/