NAME¶
aucat
—
audio files manipulation tool
SYNOPSIS¶
aucat |
[ -dn ]
[-b
size ]
[-c
min:max ]
[-e
enc ]
[-f
device ]
[-h
fmt ]
[-i
file ]
[-j
flag ]
[-o
file ]
[-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
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
s16. 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.
-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.
-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.
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 temporarly 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.
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 -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
SEE ALSO¶
audioctl(1),
cdio(1),
mixerctl(1),
audio(4),
sndio(7),
sndiod(8)
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) operation
(e.g. pipes do not support it).