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)