[CentOS-virt] Confused by "qemu-img convert"

[MargoAndTodd]

Hi All,

Okay.  Now I am confused.

I have a bunch of virtual machines running under Virtual Box 3.2.12.
I want to run them under KVM and drop Virtual Box from these
systems.

Supposedly "qemu-img convert" now supports direct conversion
from vdi to whatever KVM uses.  So I fired up the man page and
got really confused.  Then I fired up Google and got worse
confused.

Might I impose on some kind individual to write down a sample
run string that would show me how to do this?

Many thanks,
-T