Converting proprietary formats to native formats in qemu

Virtual box stores its image in vdi and vmware with vmdk format. To convert to qcow2 or raw format use the following command

qemu-img convert file.vdi -O qcow file.qcow

-O option is used to specify the format

The formats supported by qemu are

1. raw
2. cloop
3. cow [only on windows]
4. qcow
5. qcow2 [has many advantages, higly recommended]
6. vmdk
7. vdi
8. vhdx
9. vpi
10. bochs
11. dmg
12. nbd
13. parallels
14. vvfat

Remember you can convert images  only between these formats.

Reference

https://virtuallyfun.com/wordpress/2011/04/30/qemu-disk-image-conversion/

Redhat Qemu Documentation