12 years after this bug was filed, and because this is the top hit for "qemu-img" and stdin / stdout, I want to point out that this is now possible in Debian and other Linux distros using nbdcopy (in package libnbd-bin) + qemu-nbd.
To stream from any qemu format such as qcow2 out to stdout: nbdcopy -- [ qemu-nbd -f qcow2 image.qcow2 ] - | file - To stream from stdin into any qemu format such as qcow2: zcat image.gz | nbdcopy -- - [ qemu-nbd -f qcow2 output.qcow2 ]
