AUCAT(1) OpenBSD Reference Manual AUCAT(1) NAME aucat - audio server and stream manipulation tool SYNOPSIS aucat [-lnu] [-b nsamples] [-C min:max] [-c min:max] [-e enc] [-f device] [-h fmt] [-i file] [-m mode] [-o file] [-r rate] [-s socket] [-v volume] [-x policy] DESCRIPTION The aucat utility can record one input stream and store it on multiple destination files, doing the necessary conversions on the fly. It can play, convert, and mix multiple input files simultaneously. aucat also has a legacy mode that works like previous versions of aucat, which does not convert on the fly and supports playback of .au files. The options are as follows: -b nsamples The buffer size in frames. This is the number of samples that will be buffered before being played and controls the playback latency. -C min:max, -c min:max The range of channel numbers on the record or playback stream, respectively. The default is 0:1, i.e. stereo. -e enc Encoding of the playback or recording stream (see below). The default is signed, 16-bit, native byte order. -f device The audio(4) device to use for playing and/or recording. The de- fault is /dev/audio. -h fmt File format of the playback or record stream (see below). The default is auto. -i file Add this file to the list of files to play. If the option argu- ment is `-' then standard input will be used. -l Listen for incoming connections on Unix domain sockets. This al- lows clients to use aucat instead of the regular audio(4) device for audio input and output in order to share the physical device with other clients. The default socket name is default but other names can be used with the -s option. -m mode Set the server mode. Valid modes are play, rec, and duplex, for play-only, record-only, and full-duplex, respectively. The de- fault is duplex. -n Loopback mode. Instead of using an audio device, send input streams to the output, processing them on the fly. This mode is useful to mix, demultiplex, resample or reencode audio files of- fline. -o file Add this file to the list of files in which to store recorded samples. If the option argument is `-' then standard output will be used. -r rate Sample rate in Hertz of the playback or record stream. The de- fault is 44100Hz. -s socket Add the name socket to the list of sockets to listen on. socket cannot contain '/'. Meaningful in server mode only. -u Normally aucat tries to automatically determine the optimal pa- rameters for the audio device; if this option is specified, it will instead use the parameters specified by the -Ccer options. -v volume Software volume attenuation of the playback stream. The value must be between 1 and 127, corresponding to -42dB and -0dB atten- uation. In server mode, clients inherit this parameter. Reduc- ing the volume in advance reduces a client's dynamic range, but allows client volume to stay independent from the number of clients as long as their number is small enough. A good compro- mise is to use -4dB attenuation (12 volume units) for each addi- tional client expected (115 if 2 clients are expected, 103 for 3 clients, and so on). -x policy Action when the output stream cannot accept recorded data fast enough or the input stream cannot provide data to play fast enough. If the policy is ``ignore'' (the default) then samples that cannot be written are discarded and samples that cannot be read are replaced by silence. If the policy is ``sync'' then recorded samples are discarded, but the same amount of silence will be written once the stream is unblocked, in order to reach the right position in time. Similarly silence is played, but the same amount of samples will be discarded once the stream is un- blocked. If the policy is ``error'' then the stream is closed permanently. If aucat is sent SIGHUP, SIGINT or SIGTERM, it terminates recording to files. If sent SIGUSR1 or SIGUSR2, it increases or decreases debug lev- el, respectively. Settings for input files (-i), output files (-o), and sockets (-s) can be changed using the -Ccehrvx options. The last -Ccehrvx options specified before an -i, -o, or -s are applied to the corresponding file. Settings for the audio device can be changed using the -Ccer options. They apply to the audio device only if the -u option is given as well. The last -Ccer option specified before an -f is applied to device. If no audio device (-f) is specified but -u is given anyway, any -Ccer options specified before -ios options are applied both to the correspond- ing file and the default audio device; if they are specified after -ios options, they will be applied only to the default audio device. File formats are specified using the -h option. The following file for- mats are supported: raw Headerless file. This format is recommended since it has no limitations. wav Microsoft WAVE file format. There are limitations in- herent to the file format itself: not all encodings are supported, file sizes are limited to 2GB, and the file must support the lseek(2) operation (e.g. pipes do not support it). auto Try to guess, depending on the file name. Encodings are specified using the -e option. The following encodings are supported: s8 signed 8-bit u8 unsigned 8-bit s16le signed 16-bit, little endian u16le unsigned 16-bit, little endian s16be signed 16-bit, big endian u16be unsigned 16-bit, big endian s24le signed 24-bit, stored in 4 bytes, little endian u24le unsigned 24-bit, stored in 4 bytes, little endian s24be signed 24-bit, stored in 4 bytes, big endian u24be unsigned 24-bit, stored in 4 bytes, big endian s32le signed 32-bit, little endian u32le unsigned 32-bit, little endian s32be signed 32-bit, big endian u32be unsigned 32-bit, big endian s24le3 signed 24-bit, packed in 3 bytes, little endian u24le3 unsigned 24-bit, packed in 3 bytes, big endian s24be3 signed 24-bit, packed in 3 bytes, little endian u24be3 unsigned 24-bit, packed in 3 bytes, big endian s20le3 signed 20-bit, packed in 3 bytes, little endian u20le3 unsigned 20-bit, packed in 3 bytes, big endian s20be3 signed 20-bit, packed in 3 bytes, little endian u20be3 unsigned 20-bit, packed in 3 bytes, big endian s18le3 signed 18-bit, packed in 3 bytes, little endian u18le3 unsigned 18-bit, packed in 3 bytes, big endian s18be3 signed 18-bit, packed in 3 bytes, little endian u18be3 unsigned 18-bit, packed in 3 bytes, big endian SERVER MODE aucat can be used in server mode (-l) to overcome hardware limitations and allow applications to run on fixed sample rate devices or on devices supporting only unusual encodings. It is generally not desirable to have multiple instances of aucat running in server mode, so it is good prac- tice to start it thus: $ pgrep -x aucat || aucat -l This also ensures privacy by preventing other users from accessing the audio system. On multi-user machines aucat should be killed when no longer in use to make audio resources available again to others: $ pkill -x aucat Certain applications, such as synthesis software, require a low latency audio setup. To reduce the probability of buffer underruns or overruns, the renice(8) command can be used to give higher priority to aucat pro- cess to. Superuser privileges are required. For example: $ aucat -b 3500 -l $ sudo renice -n -20 -p `pgrep -x aucat` LEGACY MODE If neither -i nor -o are specified, aucat will run in legacy mode, and won't convert sample formats or sampling rates. In legacy mode, all op- tions except -f are ignored, and all other arguments are assumed to be names of files. In legacy mode aucat reads files sequentially, and writes them to the specified device. If a Sun .au header is detected it is skipped over and not copied to the audio device. aucat will attempt to play data from Sun .au files as monaural 8-bit ulaw samples with a sampling frequency of 8000 Hz. However, aucat will not fail if the audio device cannot be configured for these parameters. If a Microsoft .wav header (RIFF) is detected it is interpreted to select the right audio en- coding for playback and the data chunk of the file is copied to the audio device. If the device does not support the encoding, aucat will exit with an error. ENVIRONMENT AUCAT_DEBUG The debug level: may be a value between 0 and 4. AUDIODEVICE The audio device to use. EXAMPLES The following will mix and play two stereo streams, the first at 48kHz and the second at 44.1kHz: $ aucat -r 48000 -i file1.raw -r 44100 -i file2.raw The following will record channels 2 and 3 into one stereo file and chan- nels 6 and 7 into another stereo file using a 96kHz sampling rate for both: $ aucat -r 96000 -C 2:3 -o file1.raw -C 6:7 -o file2.raw The following will split a stereo file into two mono files: $ aucat -n -i stereo.wav -C 0:0 -o left.wav -C 1:1 -o right.wav The following will start aucat in server mode using default parameters, but will create an additional socket for output to channels 2:3 only (rear speakers on most cards): $ aucat -l -s default -c 2:3 -s rear The following will start aucat in server mode creating the default socket with low volume and an additional socket for high volume output: $ aucat -l -v 65 -s default -v 127 -s max SEE ALSO audioctl(1), cdio(1), mixerctl(1), audio(4) BUGS The aucat utility assumes non-blocking I/O for input and output streams. It will not work reliably on files that may block (ordinary files block, pipes don't). Resampling is low quality; down-sampling especially should be avoided when recording. Processing is done using 16-bit arithmetic, thus samples with more than 16 bits are rounded. 16 bits (i.e. 97dB dynamic) are largely enough for most applications though. OpenBSD 4.5 February 27, 2009 4