files manipulation tool
utility can play, record, mix, and
process audio files on the fly. During playback,
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
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.
can accept MIDI messages usable for:
- Volume control.
- Start, stop and relocate playback and recording.
The options are as follows:
- The buffer size of the audio device in frames. Default is
- The range of audio file channel numbers. The default is
0:1, i.e. stereo.
- Increase log verbosity.
- 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,
- Use this
device. Device mode and parameters are determined from audio files.
Default is default.
- 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).
- Audio file type. The following file types are supported:
- Headerless file.
- Microsoft WAV file format.
- Apple's audio interchange file format.
- Sun/NeXT audio file format.
- Try to guess, depending on the file name. This is the
- Play this audio file. If the option argument is
‘-’ then standard input will be used.
- 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
- 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
- Record into this audio file. If the option argument is
‘-’ then standard output will be used.
- 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 postion. The position is expressed as the number of
samples (at device sample rate).
- Control audio device properties through this MIDI port.
This includes per-stream volumes and the ability to synchronously start,
stop and relocate audio files.
- Sample rate in Hertz of the audio file. The default is
- 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
, it terminates recording to files.
can be controlled through MIDI
) as follows: a MIDI channel is assigned to
each stream, and the volume is changed using the standard volume controller
The master volume can be changed using the standard master volume system
All audio files are controlled by the following MMC messages:
- 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.
- Playback and/or recording is started.
- 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
instance, the following command will create two devices: the default
and a MMC-controlled one
$ 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
$ 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
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
Resampling is low quality.
There are limitations inherent to the wav
, and au
file formats: not all encodings are supported, file sizes are limited to 2GB,
and the files must support the
(e.g. pipes do not support it).