--- name: "aucat" section: "1" platform: "linux" package: "sndio" version: "1.10.0-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "openbsd"] url: "https://new.carta.tech/aucat" --- # aucat(1) audio file manipulation tool ## NAME **aucat** – audio file manipulation tool ## SYNOPSIS **aucat** \[**-dn**\] \[**-b** *size*\] \[**-c** *channels*\] \[**-e** *enc*\] \[**-f** *device*\] \[**-g** *position*\] \[**-h** *fmt*\] \[**-i** *file*\] \[**-m** *min*:*max*/*min*:*max*\] \[**-o** *file*\] \[**-p** *position*\] \[**-q** *port*\] \[**-r** *rate*\] \[**-v** *volume*\] ## DESCRIPTION The **aucat** utility can play, record, mix, and process audio files on the fly. During playback, **aucat** reads audio data concurrently from all played files, mixes it and plays the result on the device. Similarly, it stores audio data recorded from the device into corresponding files. An *off-line* mode could be used to process audio files without involving audio hardware. Processing includes: - Change the sound encoding. - Route the sound from one channel to another. - Control the per-file playback volume. Finally, **aucat** can accept MIDI messages usable for: - Volume control. - Start, stop and relocate playback and recording. The options are as follows: - **-b** *size* The buffer size of the audio device in frames. Default is 7680. - **-c** *channels* The audio file channels count. The default is 2, i.e. stereo. - **-d** Increase log verbosity. - **-e** *enc* Encoding of the audio file. The default is *s24*. Encoding names use the following scheme: signedness( *s* or *u*) followed by the precision in bits, the byte-order( *le* or *be*), the number of bytes per sample, and the alignment( *msb* or *lsb*). Only the signedness and the precision are mandatory. Examples: *u8*, *s16le*, *s24le3*, *s24le4lsb*. - **-f** *device* Use this [sndio(7)](/sndio/7.md) audio device. Device mode and parameters are determined from audio files. Default is *default*. - **-g** *position* Go to the given time position and start playback or recording there. This option is equivalent to an incoming MMC relocate message with the same position. The position is expressed as the number of samples (at device sample rate). - **-h** *fmt* Audio file type. The following file types are supported: - **raw** Headerless file. - **wav** Microsoft WAV file format. - **aiff** Apple's audio interchange file format. - **au** Sun/NeXT audio file format. - **auto** Try to guess, depending on the file name. This is the default. - **-i** *file* Play this audio file. If the option argument is ‘-’ then standard input will be used. - **-m** *min*:*max*/*min*:*max* Map the given range of source channels into the given range of destination channels. - **-n** Off-line mode. Read input files and store the result in the output files, processing them on the fly. This mode is useful to mix, demultiplex, resample or re-encode audio files off-line. It requires at least one input (**-i**) and one output (**-o**). - **-o** *file* Record into this audio file. If the option argument is ‘-’ then standard output will be used. - **-p** *position* Time offset where the beginning of the file belongs. The first sample of the file will be played or recorded when the device reaches the given position. The position is expressed as the number of samples (at device sample rate). - **-q** *port* Control audio device properties through this MIDI port. This includes per-stream volumes and the ability to synchronously start, stop and relocate audio files. - **-r** *rate* Sample rate in Hertz of the audio file. The default is **48000**. - **-v** *volume* Software volume attenuation of the file to play. The value must be between 1 and 127, corresponding to -42dB and -0dB attenuation in 1/3dB steps. The default is 127, i.e. no attenuation. On the command line, per-file parameters (**-cehmrv**) must precede the file definition (**-io**). If **aucat** is sent SIGHUP, SIGINT or SIGTERM, it terminates recording to files. ## MIDI CONTROL **aucat** can be controlled through MIDI (**-q**) as follows: a MIDI channel is assigned to each stream, and the volume is changed using the standard volume controller (number 7). The master volume can be changed using the standard master volume system exclusive message. All audio files are controlled by the following MMC messages: - relocate All files are relocated to the requested time position. If it is beyond the end of a file, the file is temporarily disabled until a valid position is requested. - start Playback and/or recording is started. - stop Playback and/or recording is stopped and all files are rewound back to the starting position. MIDI control is intended to be used together with [sndiod(8)](/sndiod/8.md). For instance, the following command will create two devices: the default *snd/default* and a MMC-controlled one *snd/default.mmc*: ``` $ sndiod -r 48000 -z 480 -s default -t slave -s mmc ``` Programs using *snd/default* behave normally, while programs using *snd/mmc* wait for the MMC start signal and start synchronously. Then, the following command will play a file on the *snd/mmc* audio device, giving full control to MIDI software or hardware connected to the *midithru/0* MIDI port: ``` $ aucat -f snd/mmc -q midithru/0 -i file.wav ``` At this stage, **aucat** will start, stop and relocate automatically following all user actions in the MIDI sequencer, assuming it's configured to transmit MMC on *midithru/0* and *snd/mmc*. Furthermore, the MIDI sequencer could be configured to use the *snd/mmc* port as MTC clock source, assured to be synchronous to playback of *file.wav*. ## EXAMPLES Mix and play two files while recording a third file: ``` $ aucat -i file1.wav -i file2.wav -o file3.wav ``` Record channels 2 and 3 into one stereo file and channels 6 and 7 into another stereo file using a 44.1kHz sampling rate for both: ``` $ aucat -r 44100 -m 2:3/0:1 -o file1.wav -m 6:7/0:1 -o file2.wav ``` Split a stereo file into two mono files: ``` $ aucat -n -i stereo.wav -c 1 -m 0:0/0:0 -o left.wav \ -m 1:1/0:0 -o right.wav ``` ## SEE ALSO [cdio(1)](/cdio/1.md), [audio(4)](/audio/4.md), [sndio(7)](/sndio/7.md), [audioctl(8)](/audioctl/8.md), [mixerctl(8)](/mixerctl/8.md), [sndiod(8)](/sndiod/8.md) ## BUGS Resampling is low quality. There are limitations inherent to the *wav*, *aiff*, and *au* file formats: not all encodings are supported, file sizes are limited to 2GB, and the files must support the [lseek(2)](/lseek/2.md) operation (e.g. pipes do not support it).