alsaloop - command-line PCM loopback


   alsaloop [-option] [cmd]


   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).


   -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.

   -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.

   -c <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:


          Known OSS attributes:

          IMIX, ALTPCM,

   -v | --verbose

          Verbose mode. Use multiple times to increase verbosity.

   -U | --xrun

          Verbose xrun profiling.

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

          Set process wake timeout.


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


   None known.


   alsaloop is by Jaroslav Kysela <>.  This document  is  by
   Jaroslav Kysela <>.

                              5 Aug 2010                       ALSALOOP(1)


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