The vmixctl program can be used to attach or detach the virtual mixer subsystem
(vmix) to/from audio devices. In addition it can be used to control vmix
related parameters such as the sampling rate to be used with the device.
By default most OSS drivers will attach virtual mixer to the primary audio device
of the sound card (or motherboard audio chip) when the device is attached.
However possible secondary audio devices (engines) will not have vmix
attached by default. In additional professional audio devices will be
attached without vmix because mixing may cause some unwanted distortion
to the signal.
ATTACHING VMIX TO AN AUDIO DEVICE
There are two forms of vmixctlattach command:
This alternative is to be used with devices that support only output or
have a single audio device file that supports full duplex.
The second form is to be used with devices that have separate output and
input device files. The "audiodev" parameter defines the output device and
the "inputdev" parameter is the device file to be used for input direction.
Note that both device files must belong to the same "physical" sound card.
In some cases it might be possible to use one sound card for playback and
another for recording. However this configuration is not supported and the
result may not be functional.
To find out the right device file names (audiodev and inputdev) you can use
the "ossinfo -a" command.
-r Disable recording functionality. By default vmix will suppor
recording if the master device(s) support it.
-p Do not preallocate client engines. By default vmix will
preallocate first 4 (out of 8) client engines when attaching
to the device. The remaining engines will be allocated
on-demand if there are more concurrent applications that
use the device.
-M Make vmix use more fragments.
-V Make client devices visible (have private device nodes under /dev).
-c <n> Preallocate <n> client engines instead of 4. However -p
option makes this option ineffective.
The virtual mixer subsystem will set the physical audio devce(s) to use
fixed sampling rate that is 48000 Hz by default. It is possible to use
"vmixctlrateaudiodev" to switch vmix to use some different rate with this
device (pair). You should use "ossinfo -a-v2" to verify that the sampling rate
is actually supported by the device. Otherwise the actual device may enforce
vmix to use the nearest supported rate (or some default rate).
The "audiodev" parameter is the device file name (see ossinfo -a) that is
used for playback. The input device name doesn't need to be specified.
Note that some professional audio devices may be locked to external sampling
rate or some fixed rate (defined in ossmix/ossxmis). In such case the rate is
not changeable by vmixctl.
DETACHING VMIX FROM AN AUDIO DEVICE
It is possible to detach vmix from an audio device if it causes problems
with applications by using "vmix detachaudiodev".
It is not possible to detach and (re)attach vmix to the same device more
than few times. Use the vmix-enable setting in the control panel
(ossxmix or ossmix) to disable/re-enable vmix if you need to do it
repeatedly. Use vmix detach only if you need to attach virtual mixer using
vmix detach /dev/oss/oss_envy240/pcm0
The control panel elements related with vmix are not removed from the
mixer API when vmix is detached. This may be somehow confusing.