vpcm is a kernel extension similar to SoundFlower (https://github.com/mattingalls/Soundflower).
Unlike SoundFlower, it does not only create virtual sound devices in your computer's GUI, but also entries for virtual devices in your computer's /dev
filesystem.
This is is useful in conjunction with existing sound tools from Linux available through Homebrew or MacPorts, or to send audio data over the network using a streaming tool like netcat
.
Once vpcm has been installed, a new device entry /dev/vpcmctl
exists in the /dev
filesystem. Using the echo
command, it is possible to send commands to the vpcm controller in order to create or delete virtual sound devices. Reading from /dev/vpcmctl
will provide you with an overview of existing vpcm devices. Sending the create
command will create a new vpcm:
$ echo create --rate=48000 --buffer-frames=1024 MyDevice >/dev/vpcmctl
$ cat /dev/vpcmctl
vpcm Virtual Audio Device, built Mar 27 2020 22:54:55
Number of device pairs: 1
"MyDevice" -> /dev/vpcm1
CoreAudio clients: 0
Device node state: closed
Configuration:
--playback
--rate=48000
--channels=2
--buffer-frames=1024
--latency-msec=0
--format=float32le
--overflow=zeros
In your computer's GUI, a new entry "MyDevice" will appear under audio devices. Choosing that for output, audio data will now be available to read from /dev/vpcm1
. This will be raw data in the format described by the device options, and may be piped into a command line tool or written to disk:
$ cat /dev/vpcm1 > myaudio.raw
The following options are available when creating a device:
--playback
or--record
to choose the direction into which the device operates.--rate=<sampling rate>
to choose the sampling rate.--channels=<number of channels>
for the number of playback or recording channels.--buffer-frames=<frames>
for the device's internal buffer size in terms of audio frames.--latency-msec=<latency>
for the device's nominal latency (used by the system when synchronizing audio and video).--format=<float32|s16>
to choose the number format used.--overflow=<zeros|noise|discard>
to specify what happens when the device is running out of data.--[no-]eof-on-idle
determines whether a pipe or output file is closed as soon as the audio engine side of the device is idle.--raw
to omit volume scaling and clipping operations on sample data.--posix-pipe
will report EPIPE (broken pipe) to I/O requests if there is no active client on the GUI side. Some command line tools require this to work if data is piped to or from a vpcm device.
Besides the create
command, a few other commands are available:
delete <GUI name>
deletes a device with given GUI name.name <GUI name>
provides the device path of the device with the given GUI name on the next read from the vpcmctl device.describe <GUI name>
provides the GUI device name, with all options, of the named device. Output will be available on the next read from the vpcmctl device.
- Open the XCode project at
Source/vpcm.xcodeproj/
- Choose Product->Build For->Running from the XCode menu
- The kext will be located at
Build/InstallerRoot/Library/Extensions/vpcm.kext
To install, copy the kext to /Library/Extensions
(not /System/Library/Extensions
).
Reboot the machine for the installation to take effect.