NAME

       alsaloop - command-line PCM loopback

SYNOPSIS

       alsaloop [-option] [cmd]

DESCRIPTION

       alsaloop allows create a PCM loopback between a PCM capture device and a PCM playback device.

       alsaloop supports multiple soundcards, adaptive clock synchronization, adaptive rate resampling using the
       samplerate  library (if available in the system). Also, mixer controls can be redirected from one card to
       another (for example Master and PCM).

OPTIONS

       -h | --help

              Prints the help information.

       -g <file> | --config=<file>

              Use given configuration file. The syntax of this file is simple: one  line  contains  the  command
              line options for one job. The '#' means comment and rest of line is ignored. Example:

                # First line - comment, second line - first job
                -C hw:1,0 -P hw:0,0 -t 50000 -T 1
                # Third line - comment, fourth line - second job
                -C hw:1,1 -P hw:0,1 -t 40000 -T 2

       -d | --daemonize

              Daemonize the main process and use syslog for messages.

       -P <device> | --pdevice=<device>

              Use given playback device.

       -C <device> | --cdevice=<device>

              Use given capture device.

       -X <device> | --pctl=<device>

              Use given CTL device for playback.

       -Y <device> | --cctl=<device>

              Use given CTL device for capture.

       -x <ctl_ascii_name> | --prateshift=<ctl_ascii_name>

              Specify ctl ascii name for playshift sync mode (see the Examples section).

       -l <latency> | --latency=<frames>

              Requested latency in frames.

       -t <usec> | --tlatency=<usec>

              Requested latency in usec (1/1000000sec).

       -f <format> | --format=<format>

              Format  specification  (usually  S16_LE  S32_LE).  Use  -h to list all formats.  Default format is
              S16_LE.

       -c <channels> | --channels=<channels>

              Channel count specification. Default value is 2.

       -r <rate> | --rate=<rate>

              Rate specification. Default value is 48000 (Hz).

       -n | --resample

              Allow rate resampling using alsa-lib.

       -A <converter> | --samplerate=<converter>

              Use libsamplerate and choose a converter:

                0 or sincbest     - best quality
                1 or sincmedium   - medium quality
                2 or sincfastest  - lowest quality
                3 or zerohold     - hold zero samples
                4 or linear       - worst quality - linear resampling
                5 or auto         - choose best method

       -B <size> | --buffer=<size>

              Buffer size in frames.

       -E <size> | --period=<size>

              Period size in frames.

       -s <secs> | --seconds=<secs>

              Duration of loop in seconds.

       -b | --nblock

              Non-block mode (very early process wakeup). Eats more CPU.

       -S <mode> | --sync=<mode>

              Sync mode specification for capture to playback stream:
                0 or none       - do not touch the stream
                1 or simple     - add or remove samples to keep
                                  both streams synchronized
                2 or captshift  - use driver for the capture device
                                  (if supported) to compensate
                                  the rate shift
                3 or playshift  - use driver for the playback device
                                  (if supported) to compensate
                                  the rate shift
                4 or samplerate - use samplerate library to do rate resampling
                5 or auto       - automatically selects the best method
                                  in this order: captshift, playshift,
                                  samplerate, simple

       -T <num> | --thread=<num>

              Thread number (-1 means create a unique thread). All jobs with same thread numbers are run  within
              one thread.

       -m <mixid> | --mixer=<midid>

              Redirect  mixer  control  from  the  playback  card  to  the  capture  card.  Format  of  mixid is
              SRCID(PLAYBACK)[@DSTID(PLAYBACK)]:

                "name='Master Playback Switch'@name='Another Switch'"
                "name='PCM Playback Volume'"

              Known attributes:

                name      - control ID name
                index     - control ID index
                device    - control ID device
                subdevice - control ID subdevice
                iface     - control ID interface
                numid     - control ID numid

       -O <ossmixid> | --ossmixer=<midid>

              Redirect mixer control from the OSS Mixer  emulation  layer  (capture  card)  to  the  ALSA  layer
              (capture card). Format of ossmixid is ALSAID[,INDEX]@OSSID:

                "Master@VOLUME"
                "PCM,1@ALTPCM"

              Known OSS attributes:

                VOLUME, BASS, TREBLE, SYNTH, PCM, SPEAKER, LINE, MIC, CD, IMIX, ALTPCM,
                RECLEV, IGAIN, OGAIN, LINE1, LINE2, LINE3, DIGITAL1, DIGITAL2, DIGITAL3,
                PHONEIN, PHONEOUT, VIDEO, RADIO, MONITOR

       -v | --verbose

              Verbose mode. Use multiple times to increase verbosity.

       -U | --xrun

              Verbose xrun profiling.

       -W <timeout> | --wake=<timeout>

              Set process wake timeout.

EXAMPLES

       alsaloop -C hw:0,0 -P hw:1,0 -t 50000

       alsaloop -C hw:soundcard,0 -P hw:Loopback,0 -t 50000 -S playshift \
       -x iface=PCM,name='PCM Rate Shift 100000',device=1

BUGS

       None known.

AUTHOR

       alsaloop is by Jaroslav Kysela <perex@perex.cz>.  This document is by Jaroslav Kysela <perex@perex.cz>.

                                                   5 Aug 2010                                        ALSALOOP(1)