sndio/aucat/aucat.1

.\"	$OpenBSD: aucat.1,v 1.73 2010/07/31 08:48:01 ratchov Exp $
.\"
.\" Copyright (c) 2006 Alexandre Ratchov <alex@caoua.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.Dd $Mdocdate: July 31 2010 $
.Dt AUCAT 1
.Os
.Sh NAME
.Nm aucat
.Nd audio server and stream manipulation tool
.Sh SYNOPSIS
.Nm aucat
.Bk -words
.Op Fl dlnu
.Op Fl a Ar flag
.Op Fl b Ar nframes
.Op Fl C Ar min : Ns Ar max
.Op Fl c Ar min : Ns Ar max
.Op Fl e Ar enc
.Op Fl f Ar device
.Op Fl h Ar fmt
.Op Fl i Ar file
.Op Fl j Ar flag
.Op Fl m Ar mode
.Op Fl o Ar file
.Op Fl q Ar device
.Op Fl r Ar rate
.Op Fl s Ar name
.Op Fl t Ar mode
.Op Fl U Ar unit
.Op Fl v Ar volume
.Op Fl x Ar policy
.Op Fl z Ar nframes
.Ek
.Sh DESCRIPTION
.Nm
is an audio utility which can simultaneously play and record
any number of audio
.Em streams
on any number of audio devices,
possibly controlled through MIDI.
It can also act as an audio server, in which case streams
correspond to client connections rather than plain files.
.Pp
Audio devices are independent.
A list of streams is attached to each audio device,
as well as an optional list of MIDI ports to control the device.
A typical invocation of
.Nm
consists in providing streams to play and record,
and possibly the audio device to use, if the default is not desired.
.Pp
This also applies to server mode, except that streams are created
dynamically when clients connect to the server.
Thus, instead of actual streams (paths to plain files),
templates for client streams (sub-device names) must be provided.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl a Ar flag
Control whether
.Nm
opens the audio device only when needed or keeps it open all the time.
If the flag is
.Va on
then the device is kept open all the time, ensuring no other program can
steal it.
If the flag is
.Va off ,
then it's automatically closed, allowing other programs to have direct
access to the device, or the device to be disconnected.
The default is
.Va on .
.It Fl b Ar nframes
The buffer size of the audio device in frames.
A frame consists of one sample for each channel in the stream.
This is the number of frames that will be buffered before being played
and thus controls the playback latency.
.It Xo
.Fl C Ar min : Ns Ar max ,
.Fl c Ar min : Ns Ar max
.Xc
The range of stream channel numbers for recording and playback directions,
respectively.
The default is 0:1, i.e. stereo.
.It Fl d
Increase log verbosity.
.Nm
logs on stderr until it daemonizes.
.It Fl e Ar enc
Encoding of the playback or recording stream (see below).
The default is signed, 16-bit, native byte order.
.It Fl f Ar device
Add this
.Xr sndio 7
audio device to devices used for playing and/or recording.
Preceding streams
.Pq Fl ios ,
control MIDI ports
.Pq Fl q ,
and per-device options
.Pq Fl abz
apply to this device.
Device mode and parameters are determined from streams
attached to it.
.It Fl h Ar fmt
File format of the playback or record stream (see below).
The default is auto.
.It Fl i Ar file
Add this file to the list of streams to play.
If the option argument is
.Sq -
then standard input will be used.
.It Fl j Ar flag
Control whether stream channels are joined or expanded if
the stream number of channels is not equal to the device number of channels.
If the flag is
.Va off
then stream channels are routed to the corresponding
device channel, possibly discarding channels not present in the device.
If the flag is
.Va on ,
then a single stream channel may be sent on multiple device channels,
or multiple stream channels may be sent to a single device channel.
For instance, this feature could be used to request mono streams to
be sent on multiple outputs or to record a stereo input into a mono stream.
The default is
.Ar on .
.It Fl l
Detach and become a daemon.
.It Fl m Ar mode
Set the stream mode.
Valid modes are
.Ar play ,
.Ar rec ,
and
.Ar mon ,
corresponding to playback, recording and monitoring.
A monitoring stream is a fake recording stream corresponding to
the mix of all playback streams.
Multiple modes can be specified, separated by commas,
but the same stream cannot be used for both recording and monitoring.
The default is
.Ar play , Ns Ar rec
(i.e. full-duplex).
.It Fl n
Loopback mode.
Instead of using audio devices, send input streams
to the output, processing them on the fly.
This mode is useful to mix, demultiplex, resample or reencode
audio files offline.
.It Fl o Ar file
Add this file to the list of recording streams.
If the option argument is
.Sq -
then standard output will be used.
.It Fl q Ar device
Expose the audio device clock on this
.Xr sndio 7
MIDI port and allow audio device properties to be controlled
through MIDI.
This includes per-stream volumes and the ability to
synchronously start, stop and relocate streams created in
MIDI Machine
Control (MMC) slave mode
.Pq Fl t .
.It Fl r Ar rate
Sample rate in Hertz of the stream.
The default is 44100Hz.
.It Fl s Ar name
Add
.Ar name
to the list of sub-devices to expose in server mode.
This allows clients to use
.Nm
instead of the physical audio device for audio input and output
in order to share the physical device with other clients.
Defining multiple sub-devices allows splitting a physical audio device
into logical devices having different properties (e.g. channel ranges).
The given
.Ar name
corresponds to the
.Dq option
part of the
.Xr sndio 7
device name string.
.It Fl t Ar mode
Select the way streams are controlled by MIDI Machine Control (MMC)
messages.
If the mode is
.Va off
(the default), then streams are not affected by MMC messages.
If the mode is
.Va slave ,
then streams are started synchronously by MMC start messages;
additionally, the server clock is exposed as MIDI Time Code (MTC)
messages allowing MTC-capable software or hardware to be synchronized
to audio streams.
.It Fl U Ar unit
Unit number to use when running in server mode.
Each
.Nm
server instance has an unique unit number,
used in
.Xr sndio 7
device names.
The default is 0.
.It Fl u
Normally
.Nm
tries to automatically determine the optimal parameters for the audio device;
if this option is specified,
it will instead use the parameters specified by the
.Fl Ccer
options.
.It Fl v Ar volume
Software volume attenuation of the playback stream.
The value must be between 1 and 127,
corresponding to \-42dB and \-0dB attenuation.
In server mode, clients inherit this parameter.
Reducing 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 compromise is to use \-4dB attenuation (12 volume units)
for each additional client expected
(115 if 2 clients are expected, 103 for 3 clients, and so on).
.It Fl x Ar 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
.Dq 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
.Dq 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 unblocked.
If the policy is
.Dq error
then the stream is closed permanently.
.Pp
If a stream is created with the
.Fl t
option,
the
.Dq ignore
action is disabled for any stream connected to it
to ensure proper synchronization.
.It Fl z Ar nframes
The audio device block size in frames.
This is the number of frames between audio clock ticks,
i.e. the clock resolution.
If a stream is created with the
.Fl t
option,
and MTC is used for synchronization, the clock
resolution must be 96, 100 or 120 ticks per second for maximum
accuracy.
For instance, 120 ticks per second at 48000Hz corresponds
to a 400 frame block size.
.El
.Pp
On the command line,
per-device parameters
.Pq Fl abz
must precede the device definition
.Pq Fl f ,
and per-stream parameters
.Pq Fl Ccehjmrtvx
must precede the stream definition
.Pq Fl ios .
MIDI ports
.Pq Fl q
and streams definitions
.Pq Fl ios
must precede the definition of the device
.Pq Fl f
to which they are attached.
Global parameters
.Pq Fl dlnu
are position-independent.
.Pp
If no audio devices
.Pq Fl f
are specified,
settings are applied as if
the default device is specified as the last argument.
If no streams
.Pq Fl ios
are specified for a device, a default server sub-device is
created attached to it, meaning that
.Nm
behaves as an audio server.
The default
.Xr sndio 7
device is
.Pa aucat:0
.Pq also known as Pa aucat:0.default
.Pp
If
.Nm
is sent
.Dv SIGHUP ,
.Dv SIGINT
or
.Dv SIGTERM ,
it terminates recording to files.
.Pp
File formats are specified using the
.Fl h
option.
The following file formats are supported:
.Bl -tag -width s32lexxx -offset indent
.It raw
Headerless file.
This format is recommended since it has no limitations.
.It wav
Microsoft WAVE file format.
There are limitations inherent to the file format itself:
not all encodings are supported,
file sizes are limited to 2GB,
and the file must support the
.Xr lseek 2
operation (e.g. pipes do not support it).
.It auto
Try to guess, depending on the file name.
.El
.Pp
Encodings are specified using the
.Fl e
option.
The following encodings are supported:
.Pp
.Bl -tag -width s32lexxx -offset indent -compact
.It s8
signed 8-bit
.It u8
unsigned 8-bit
.It s16le
signed 16-bit, little endian
.It u16le
unsigned 16-bit, little endian
.It s16be
signed 16-bit, big endian
.It u16be
unsigned 16-bit, big endian
.It s24le
signed 24-bit, stored in 4 bytes, little endian
.It u24le
unsigned 24-bit, stored in 4 bytes, little endian
.It s24be
signed 24-bit, stored in 4 bytes, big endian
.It u24be
unsigned 24-bit, stored in 4 bytes, big endian
.It s32le
signed 32-bit, little endian
.It u32le
unsigned 32-bit, little endian
.It s32be
signed 32-bit, big endian
.It u32be
unsigned 32-bit, big endian
.It s24le3
signed 24-bit, packed in 3 bytes, little endian
.It u24le3
unsigned 24-bit, packed in 3 bytes, big endian
.It s24be3
signed 24-bit, packed in 3 bytes, little endian
.It u24be3
unsigned 24-bit, packed in 3 bytes, big endian
.It s20le3
signed 20-bit, packed in 3 bytes, little endian
.It u20le3
unsigned 20-bit, packed in 3 bytes, big endian
.It s20be3
signed 20-bit, packed in 3 bytes, little endian
.It u20be3
unsigned 20-bit, packed in 3 bytes, big endian
.It s18le3
signed 18-bit, packed in 3 bytes, little endian
.It u18le3
unsigned 18-bit, packed in 3 bytes, big endian
.It s18be3
signed 18-bit, packed in 3 bytes, little endian
.It u18be3
unsigned 18-bit, packed in 3 bytes, big endian
.El
.Sh SERVER MODE
If at least one sub-device
.Pq Fl s
is exposed by
.Nm ,
including the case when no stream options are given,
then
.Nm
can be used as a server
to overcome hardware limitations and allow applications
to run on fixed sample rate devices or on devices
supporting only unusual encodings.
.Pp
Certain applications, such as synthesis software,
require a low latency audio setup.
To reduce the probability of buffer underruns or overruns, especially
on busy machines, the server can be started by the super-user, in which
case it will run with higher priority.
Any user will still be able to connect to it,
but for privacy reasons only one user may have
connections to it at a given time.
.Sh MIDI CONTROL
.Nm
can expose the audio device clock on registered
MIDI ports
.Pq Fl q
and allows audio device properties to be controlled
through MIDI.
If running in server mode
.Nm
creates a MIDI port with the same name as the default audio
device to which MIDI programs can connect.
.Pp
A MIDI channel is assigned to each stream, and the volume
is changed using the standard volume controller (number 7).
Similarly, when the audio client changes its volume,
the same MIDI controller message is sent out; it can be used
for instance for monitoring or as feedback for motorized
faders.
.Pp
Streams created with the
.Fl t
option are controlled by the following MMC messages:
.Bl -tag -width relocateXXX -offset indent
.It relocate
Streams are relocated to the requested time postion
relative to the beginning of the stream, at which playback
and recording must start.
If the requested position is beyond the end of file,
the stream is temporarly disabled until a valid postion is requested.
This message is ignored by client streams (server mode).
The given time position is sent to MIDI ports as an MTC
.Dq "full frame"
message forcing all MTC-slaves to relocate to the given
position (see below).
.It start
Put all streams in starting mode.
In this mode,
.Nm
waits for all streams to become ready
to start, and then starts them synchronously.
Once started, new streams can be created (server mode)
but they will be blocked
until the next stop-to-start transition.
.It stop
Put all streams in stopped mode (the default).
In this mode, any stream attempting to start playback or recording
is paused.
Files are stopped and rewound back to the starting position,
while client streams (server mode) that are already
started are not affected until they stop and try to start again.
.El
.Pp
Streams created with the
.Fl t
option export the server clock using MTC, allowing non-audio
software or hardware to be synchronized to the audio stream.
The following sample rates
.Pq Fl r
and block sizes
.Pq Fl z
are recommended for maximum accuracy:
.Pp
.Bl -bullet -offset indent -compact
.It
44100Hz, 441 frames
.It
48000Hz, 400 frames
.It
48000Hz, 480 frames
.It
48000Hz, 500 frames
.El
.Pp
For instance, the following command will create two devices:
the default
.Va aucat:0
and a MIDI-controlled
.Va aucat:0.mmc :
.Bd -literal -offset indent
$ aucat -l -r 48000 -z 400 -s default -t slave -s mmc
.Ed
.Pp
Streams connected to
.Va aucat:0
behave normally, while streams connected to
.Va aucat:0.mmc
wait for the MMC start signal and start synchronously.
Regardless of which device a stream is connected to,
its playback volume knob is exposed.
.Pp
For instance, the following command will play a file on the
.Va aucat:0.mmc
audio device, and give full control to MIDI software or hardware
connected to the
.Va midithru:0
MIDI device:
.Bd -literal -offset indent
$ aucat -t slave -q midithru:0 -i file.wav -f aucat:0.mmc
.Ed
.Pp
At this stage,
.Nm
will start, stop and relocate automatically following all user
actions in the MIDI sequencer.
Note that the sequencer must use
.Va aucat:0
as the MTC source, i.e. the audio server, not the audio player.
.Sh ENVIRONMENT
.Bl -tag -width "AUDIODEVICE" -compact
.It Ev AUDIODEVICE
.Xr sndio 7
audio device to use if the
.Fl f
option is not specified.
.El
.Sh EXAMPLES
The following will mix and play two stereo streams,
the first at 48kHz and the second at 44.1kHz:
.Bd -literal -offset indent
$ aucat -r 48000 -i file1.raw -r 44100 -i file2.raw
.Ed
.Pp
The following will record channels 2 and 3 into one stereo file and
channels 6 and 7 into another stereo file using a 96kHz sampling rate for
both:
.Bd -literal -offset indent
$ aucat -r 96000 -C 2:3 -o file1.raw -C 6:7 -o file2.raw
.Ed
.Pp
The following will split a stereo file into two mono files:
.Bd -literal -offset indent
$ aucat -n -i stereo.wav -C 0:0 -o left.wav -C 1:1 -o right.wav
.Ed
.Pp
The following will start
.Nm
in server mode using default parameters, but will create an
additional sub-device for output to channels 2:3 only (rear speakers
on most cards), exposing the
.Pa aucat:0
and
.Pa aucat:0.rear
devices:
.Bd -literal -offset indent
$ aucat -l -s default -c 2:3 -s rear
.Ed
.Pp
The following will start
.Nm
in server mode creating the default sub-device with low volume and
an additional sub-device for high volume output, exposing the
.Pa aucat:0
and
.Pa aucat:0.max
devices:
.Bd -literal -offset indent
$ aucat -l -v 65 -s default -v 127 -s max
.Ed
.Pp
The following will start
.Nm
in server mode configuring the audio device to use
a 48kHz sample frequency, 240-frame block size,
and 2-block buffers.
The corresponding latency is 10ms, which is
the time it takes the sound to propagate 3.5 meters.
.Bd -literal -offset indent
$ aucat -l -r 48000 -b 480 -z 240
.Ed
.Sh SEE ALSO
.Xr audioctl 1 ,
.Xr cdio 1 ,
.Xr mixerctl 1 ,
.Xr audio 4 ,
.Xr sndio 7
.Sh BUGS
The
.Nm
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).
To avoid audio underruns/overruns or MIDI jitter caused by file I/O,
it's recommended to use two
.Nm
processes: a server handling audio and MIDI I/O and a client handling
disk I/O.
.Pp
Resampling is low quality; down-sampling especially should be avoided
when recording.
.Pp
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.
.Pp
If
.Fl a Ar off
is used in server mode,
.Nm
creates sub-devices to expose first
and then opens the audio hardware on demand.
Technically, this allows
.Nm
to attempt to use one of the sub-devices it exposes as audio device,
creating a deadlock.
To avoid this,
.Fl a Ar off
is disabled for the default audio device, but nothing prevents the user
from shooting himself in the foot by creating a similar deadlock.