alsaloop -V (return code: 1)
alsaloop: unrecognized option '--version'
ALSA lib pcm_hw.c:1700:(_snd_pcm_hw_open) Invalid value for card
playback hw:0,0 open error: No such file or directory
Loopback initialization failure.
alsaloop --help (return code: 0)
Usage: alsaloop [OPTION]...
-h,--help help
-g,--config configuration file (one line = one job specified)
-d,--daemonize daemonize the main process and use syslog for errors
-P,--pdevice playback device
-C,--cdevice capture device
-X,--pctl playback ctl device
-Y,--cctl capture ctl device
-l,--latency requested latency in frames
-t,--tlatency requested latency in usec (1/1000000sec)
-f,--format sample format
-c,--channels channels
-r,--rate rate
-n,--resample resample in alsa-lib
-A,--samplerate use converter (0=sincbest,1=sincmedium,2=sincfastest,
3=zerohold,4=linear)
-B,--buffer buffer size in frames
-E,--period period size in frames
-s,--seconds duration of loop in seconds
-b,--nblock non-block mode (very early process wakeup)
-S,--sync sync mode(0=none,1=simple,2=captshift,3=playshift,4=samplerate,
5=auto)
-a,--slave stream parameters slave mode (0=auto, 1=on, 2=off)
-T,--thread thread number (-1 = create unique)
-m,--mixer redirect mixer, argument is:
SRC_SLAVE_ID(PLAYBACK)[@DST_SLAVE_ID(CAPTURE)]
-O,--ossmixer rescan and redirect oss mixer, argument is:
ALSA_ID@OSS_ID (for example: "Master@VOLUME")
-e,--effect apply an effect (bandpass filter sweep)
-v,--verbose verbose mode (more -v means more verbose)
-w,--workaround use workaround (serialopen)
-U,--xrun xrun profiling
-W,--wake process wake timeout in ms
-z,--syslog use syslog for errors
Recognized sample formats are: S8 U8 S16_LE S16_BE U16_LE U16_BE S24_LE S24_BE U24_LE U24_BE S32_LE S32_BE U32_LE U32_BE FLOAT_LE FLOAT_BE FLOAT64_LE FLOAT64_BE IEC958_SUBFRAME_LE IEC958_SUBFRAME_BE MU_LAW A_LAW IMA_ADPCM MPEG GSM SPECIAL S24_3LE S24_3BE U24_3LE U24_3BE S20_3LE S20_3BE U20_3LE U20_3BE S18_3LE S18_3BE U18_3LE U18_3BE G723_24 G723_24_1B G723_40 G723_40_1B DSD_U8 DSD_U16_LE DSD_U32_LE DSD_U16_BE
Tip #1 (usable 500ms latency, good CPU usage, superb xrun prevention):
alsaloop -t 500000
Tip #2 (superb 1ms latency, but heavy CPU usage):
alsaloop -t 1000