- Input Muplexer audio driver.
IMUX is a virtual recording engine that permits up to 8 audio recording
applications to run at the same time. Generally most soundcards permit only a
single recording application to record the input source (via mic, line or CD).
With IMUX, you can use up to 8 recording applications to record the same
source in different sample rates, bits/sample and channels (mono/stereo). IMUX
does all the rate and format conversion in software. The applications think
that they are actually getting data from the physical device. For instance, if
you want to record the input from a CDROM in .wav format at 48Khz/8/Mono and
at the same time you want to record the same stream in .mp3 format in 44.1Khz
16 bit stereo, with IMUX, you can start the wave recording application on the
first IMUX device and start the MP3 encoder on the second IMUX device and both
applications will run simultaneously thinking that they are getting data from
the physical soundcard.
To add the IMUX driver you first need to ensure that there is a physical
soundcard present and then you can run ossdetect -i
to add it. You may
want to select a master device by setting imux_masterdev, but the
autodetection should provide a good default. After OSS restart, imux should be
Connect an input source to the soundcard's line-in jack. Using the Mixer app
like ossmix (or any OSS compliant mixer) set the recording source to Line-In
(eg ossmix line.rec ON) Now you can start recording the input in multiple
formats and at different sample rates. The simplest example is:
ossrecord -s48000 -b16 -c2 -d/dev/oss/oss_imux0/pcmin0 test1.wav &
ossrecord -s8000 -b8 -d/dev/oss/oss_imux0/pcmin0 test2.wav &
After a few minutes of recording you can stop them by placing the command in
forground mode (type fg %1 or fg %2) and press ^c to stop.
You now have two wav format files. test1.wav is a 48KHz 16bit stereo file and
test2.wav is a 8Khz 8bit Mono file.
You can now playback the files as follows:
- ossplay -v test1.wav and it should show you that the
file is indeed 48Khz 16bit stereo.
- ossplay -v test2.wav - you should see that this file
is indeed a 8Khz 8bit mono file.
What you have essentially accomplished is recording a single input stream into
two different formats at the same time.
You can now extend this analogy to record the input in mp3 format and RealAudio
The IMUX control panel can be displayed by typing ossxmix -d
mixer number> (for e.g. in the above example, IMUX mixer is #2 so we type
There are record level control sliders for each input channel and it will show
activity when a recording program is active on a particular channel.
- imux_masterdev: Selects which physical device to use as the
Master device for the IMUX driver. Values: -1: automatically
selected by OSS, 1-N: Audio device index of the master device (as reported
by ossinfo -a), Default: -1.
- imux_rate: Specifies what is the base sampling rate used by
the imux driver. Values: 5000-96000 Default: 48000
- imux_devices: Specifies number of Input Multiplexer devices
to setup. Values: 2-48 Default: 5
/etc/oss4/conf/oss_imux.conf Device configuration file