vmixctl

Section: OSS System Administration Commands (8) Updated: 31 July 2010 Local index Up

NAME

vmixctl - Open Sound System utility to control the vmix subsystem.

SYNOPSIS

o       vmixctl attach [attach_options...] audiodev [inputdev]
o       vmixctl detach [attach_options...] audiodev
o       vmixctl rate audiodev samplerate

DESCRIPTION

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 vmixctl attach command:

o: vmixctl attach audiodev This alternative is to be used with devices that support only output or have a single audio device file that supports full duplex.
o: vmixctl attach audiodev inputdev 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.

ATTACH OPTIONS

o: -r Disable recording functionality. By default vmix will suppor recording if the master device(s) support it.
o: -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.
o: -M Make vmix use more fragments.
o: -V Make client devices visible (have private device nodes under /dev).
o: -c <n> Preallocate <n> client engines instead of 4. However -p option makes this option ineffective.

EXAMPLES

o: vmixctl attach /dev/oss/oss_envy240/pcm0
o: vmixctl attach /dev/oss/oss_envy240/pcm0 /dev/oss/oss_envy240/pcmin0

SETTING THE SAMPLING RATE USED BY VMIX

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 "vmixctl rate audiodev" 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.

EXAMPLE

o: vmixctl rate /dev/oss/oss_envy240/pcm0

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 detach audiodev".

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 different parameters.