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VIRTUAL_OSS(8) System Manager's Manual VIRTUAL_OSS(8) NAME virtual_oss -- daemon to multiplex and demultiplex an OSS device SYNOPSIS virtual_oss [-h] DESCRIPTION virtual_oss is an audio mixing application that multiplexes and demulti- plexes a single OSS device into multiple customizable OSS compatible de- vices using character devices from userspace. These devices can be used to record played back audio and mix the individual channels in multiple ways. virtual_oss requires the cuse(3) kernel module. To load the driver as a module at boot time, place the following line in loader.conf(5): cuse_load="YES" All channel numbers start at zero. Left channel is zero and right channel is one. The following options are available: -B Run program in background. -S Enable automatic DSP rate resampling. -Q quality Set resampling quality: 0=best, 1=medium and 2=fastest (default). -b bits Set sample depth to bits for the subsequent commands. Valid values are 8, 16, 24 and 32. -r rate Set default sample-rate for the subsequent commands. -s value Set default buffer size to value. If the argument is suffixed by "ms" it is interpreted as milliseconds. Else the argument gives number of samples. The buffer size specified is per channel. If there are multiple channels, the total buffer size will be larger. -i priority Set real-time priority to priority. Refer to rtprio(1) for more information. -a log2_amp Set the default DSP output and input device amplification to log2_amp. The specified amplification is logarithmic. Valid val- ues range from -63 to 63 inclusivly. The device input amplifica- tion gets set to minus log2_amp and the device output amplification gets set to log2_amp. -a i,log2_amp Set the default DSP input device amplification to log2_amp. The specified amplification is logarithmic. Valid values range from -63 to 63 inclusivly. -a o,log2_amp Set default DSP output device amplification to log2_amp. The spec- ified amplification is logarithmic. Valid values range from -63 to 63 inclusivly. -p polarity Set default polarity of DSP device. A value of zero means normal polarity. A value of one means negative polarity. -e rx_mute,tx_mute Set default mute state of DSP device. A value of zero means un- muted. A value of one means muted. -m rx_ch,tx_ch,.... Set default channel mapping of DSP device, as a comma separated list of integers. The first integer selects the receive channel, the second value selects the transmit channel and then it repeats. A value of zero indicates the first receive or transmit channel. -C num Set the maximum number of mix channels to num. -c num Set mix channels for the subsequent commands. -M type,src_ch,dst_ch,pol,mute,log2_gain Add a monitoring filter. The filter consists of a list of comma separated arguments. The first argument indicates the type of mon- itoring filter: i Feedback one mix input channel into another mix output channel, for remote feedback. o Add one mix output channel into another mix output channel, for creating a mix of multiple output channels. x Feedback one mix output channel into another mix input channel, for local feedback. The second argument gives the source mix channel. The third argu- ment gives the destination mix channel. The fourth argument gives the polarity, default is zero. The fifth argument gives the mute state, default is one or muted. The sixth argument gives the am- plitude, default is zero or no gain. -t devname Set control device name. -P devname Set playback DSP device only. Specifying /dev/null is magic and means no playback device. Specifying a sndio(7) device descriptor prefixed by "/dev/sndio/" is also magic, and will use a sndio back- end rather than an OSS device. -O devname Set playback DSP device only which acts as a master device. This option is used in conjunction with -R /dev/null . -R devname Set recording DSP device only. Specifying /dev/null is magic and means no recording device. -f devname Set both playback and recording DSP device -w name Create a WAV file format compatible companion device by given name. This option should be specified before the -d and -l options. -d name Create an OSS device by given name. -l name Create a loopback OSS device by given name. -L name Create a loopback OSS device which acts as a master device. This option is used in conjunction with -f /dev/null . -F size Set receive filter size in number of samples or <milliseconds>ms for the next device to be created. -G size Set transmit filter size in number of samples or <milliseconds>ms for the next device to be created. -D file Write process ID of virtual_oss to file. -g knee,attack,decay Enable device compressor in receive direction. See description of -x option. -x knee,attack,decay Enable output compressor and set knee, attack and decay. Knee is in the range 0..255, while attack and decay are between 0 and 62. Samples having an absolute value lower than the knee are transmit- ted unchanged. Sample values over the knee are lowered "a little bit". You can think about attack and decay as a measure of how fast or slow the gain of the compressor will work. It is advised that attack is low, so it reacts fast once too high sample values appear. It is also advised that the decay value is higher than the attack value so that the gain reduction is gradually removed. The reasoning behind this is that the compressor should react almost immediately when high volume signals arrive to protect the hard- ware, but it slowly changes gain when there are no loud signals to avoid distorting the signal. The default values are 85,3,20 . -E enable_recording If the value passed is non-zero, recording is enabled. Else recording is disabled. This can be used to synchronize multiple recording streams. -h Show usage and all available options. EXAMPLES Split a 2-channel OSS compatible sound device into multiple subdevices: virtual_oss \ -S \ -c 2 -r 48000 -b 16 -s 4ms -f /dev/dspX \ -a 0 -b 16 -c 2 -m 0,0,1,1 -d vdsp.zyn \ -a 0 -b 16 -c 2 -m 0,0,1,1 -d vdsp.fld \ -a 0 -b 16 -c 2 -m 0,0,1,1 -d dsp \ -a 0 -b 16 -c 2 -m 0,0,1,1 -w vdsp.jack.wav -d vdsp.jack \ -a 0 -b 16 -c 2 -m 0,0,1,1 -w vdsp.rec.wav -l vdsp.rec \ -M i,0,0,0,1,0 \ -M i,0,0,0,1,0 \ -M i,0,0,0,1,0 \ -M i,0,0,0,1,0 \ -t vdsp.ctl Split an 8-channel 24-bit OSS compatible sound device into multiple subde- vices: sysctl dev.pcm.X.rec.vchanformat=s24le:7.1 sysctl dev.pcm.X.rec.vchanrate=48000 sysctl dev.pcm.X.play.vchanformat=s24le:7.1 sysctl dev.pcm.X.play.vchanrate=48000 sysctl dev.pcm.X.bitperfect=1 mixer vol.volume=1 pcm.volume=1 virtual_oss \ -S \ -i 8 \ -x 85,3,20 \ -C 16 -c 8 -r 48000 -b 32 -s 4ms -f /dev/dspX \ -a 12 -b 16 -c 2 -m 0,4,1,5 -d dsp \ -a 12 -b 16 -c 2 -m 8,8,9,9 -d vdsp \ -a 13 -b 16 -c 2 -m 10,10,11,11 -d vdsp.fld \ -a 0 -b 32 -c 4 -m 4,2,5,3,6,4,7,5 -d vdsp.jack \ -a -3 -b 32 -c 2 -m 14,14,15,15 -d vdsp.zyn \ -e 0,1 \ -a 0 -b 32 -c 8 -m 0,8,1,9,2,8,3,9,4,8,5,9,6,8,7,9 -w vdsp.rec.mic.wav -d vdsp.rec.mic \ -a 0 -b 32 -c 2 -m 0,8,1,9 -w vdsp.rec.master.wav -d vdsp.master.mic \ -a 0 -b 32 -c 2 -m 10,10,11,11 -w vdsp.rec.fld.wav -l vdsp.rec.fld \ -a 0 -b 32 -c 2 -m 12,12,13,13 -w vdsp.rec.jack.wav -l vdsp.rec.jack \ -a 0 -b 32 -c 2 -m 14,14,15,15 -w vdsp.rec.zyn.wav -l vdsp.rec.zyn \ -M o,8,0,0,0,0 \ -M o,9,1,0,0,0 \ -M o,10,0,0,0,0 \ -M o,11,1,0,0,0 \ -M o,12,0,0,0,0 \ -M o,13,1,0,0,0 \ -M o,14,0,0,0,0 \ -M o,15,1,0,0,0 \ -M i,14,14,0,1,0 \ -M i,15,15,0,1,0 \ -M x,8,0,0,1,0 \ -M x,8,1,0,1,0 \ -t vdsp.ctl Create a secondary audio device sending its output audio into both input and output channels of the main DSP device. virtual_oss \ -C 4 -c 2 \ -r 48000 \ -b 24 \ -s 4ms \ -f /dev/dsp3 \ -c 2 \ -d dsp \ -m 2,2,3,3 \ -d dsp.speech \ -M o,2,0,0,0,0 \ -M o,3,1,0,0,0 \ -M x,2,0,0,0,0 \ -M x,3,1,0,0,0 Connect to a bluetooth audio headset, playback only: virtual_oss \ -C 2 -c 2 -r 48000 -b 16 -s 4ms \ -R /dev/null -P /dev/bluetooth/xx:xx:xx:xx:xx:xx -d dsp Connect to a bluetooth audio headset, playback and recording: virtual_oss \ -C 2 -c 2 -r 48000 -b 16 -s 4ms \ -f /dev/bluetooth/xx:xx:xx:xx:xx:xx -d dsp Create recording device which outputs a WAV-formatted file: virtual_oss \ -C 2 -c 2 -r 48000 -b 16 -s 4ms \ -f /dev/dspX -w dsp.wav -d dsp Create a device named dsp.virtual which mix the samples written by all clients and outputs the result for further processing into dsp.virtual_out: virtual_oss \ -S -Q 0 -b 16 -c 2 -r 96000 -s 100ms -i 20 \ -f /dev/null -d dsp.virtual -L dsp.virtual_out Create a playback-only audio device which sends its output to a remote sndio(7) server: virtual_oss \ -b 16 -c 2 -r 44100 -s 50ms \ -R /dev/null -O /dev/sndio/snd@remotehost/0 -d dsp Create a full-duplex audio device exchanging audio using the default sndio(7) server: virtual_oss -S -b 16 -C 2 -c 2 -r 48000 -s 4ms \ -f /dev/sndio/default -d dsp NOTES All character devices are created using the 0666 mode which gives everyone in the system access. SEE ALSO cuse(3), sound(4), loader.conf(5), sndio(7), mixer(8), sysctl(8), vir- tual_bt_speaker(8), virtual_equalizer(8), virtual_oss_cmd(8) AUTHORS virtual_oss was written by Hans Petter Selasky hselasky@freebsd.org. FreeBSD ports 15.quarterly April 17, 2026 VIRTUAL_OSS(8)
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | NOTES | SEE ALSO | AUTHORS
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