flapjack is a command line utility to control the Belkin USB KVM switch with audio.
Right now, to use flapjack, you have to get the Linux kernel to present the Flip KVM as a hiddev device. This requires (as of kernel 188.8.131.52) a change to the blacklist in hiddev.c, adding the HID_QUIRK_HIDDEV to the product/vendor code 0x050d/0x3201.
By default, flapjack will scan the /dev directory to try to find the hiddev device file corresponding with the Belkin Flip vendor and product ID. If it doesn't find the file, then it will fail.
This can be overriden by either specifing a file, e.g.
$ flapjack -f /dev/usb/hiddev0 -c both
or by specifying an alternate devices directory to scan, e.g.
$ flapjack -F /mydevdri -c both
The Belking Flip KVM can flip only audio, only video, or both. These options are selected with the -c option, to which is supplied (surprisingly enough) "audio", "video" or "both".
See the info page for more information.