Unlike ISO installations, deploying from a pre-configured windows 8.1 qcow2 image saves you from the tedious 30-minute setup process. However, finding a proper guide that bridges the gap between a raw ISO and a functional QCOW2 image is rare.
qemu-img info windows81.qcow2 To increase the disk size to 80GB: windows 81 qcow2 install
qemu-img convert -f vdi -O qcow2 Windows8.1.vdi windows81.qcow2 From a VMDK (VMware): Unlike ISO installations