aucat —
audio
files manipulation tool
| aucat |
[-dn]
[-b
size]
[-c
min:max]
[-e
enc]
[-f
device]
[-g
position]
[-h
fmt]
[-i
file]
[-j
flag]
[-o
file]
[-p
position]
[-q
port]
[-r
rate]
[-v
volume] |
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
min:max
- The range of audio file channel numbers. The default is
0:1, 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) 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.
-
-j
flag
- Control whether source channels are joined or expanded if
they don't match the destination number of channels. If the flag is
off, then each source channel is routed to a
single destination channel, possibly discarding channels. If the flag is
on, then a single source may be sent to
multiple destinations and multiple sources may be mixed into a single
destination. For instance, this feature could be used to convert a stereo
file into a mono file mixing left and right channels together. The default
is off.
- -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 (
-cehjrv)
must precede the file definition (
-io).
If
aucat is sent
SIGHUP,
SIGINT or
SIGTERM, it terminates recording to files.
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). For instance, the following command
will create two devices: the default
snd/0
and a MMC-controlled one
snd/0.mmc:
$ sndiod -r 48000 -z 480 -s default -t slave -s mmc
Programs using
snd/0 behave normally, while
programs using
snd/0.mmc wait for the MMC
start signal and start synchronously. Then, the following command will play a
file on the
snd/0.mmc audio device, giving
full control to MIDI software or hardware connected to the
midithru/0 MIDI port:
$ aucat -f snd/0.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.
Furthermore, the MIDI sequencer could be configured to use the
snd/0 port as MTC clock source, assured to be
synchronous to playback of
file.wav.
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 -c 2:3 -o file1.wav -c 6:7 -o file2.wav
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
cdio(1),
audio(4),
sndio(7),
audioctl(8),
mixerctl(8),
sndiod(8)
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) operation
(e.g. pipes do not support it).