alsa-utils/axfer/axfer-transfer.1

.TH AXFER\-TRANSFER 1 "28 November 2018" "alsa\-utils"

.SH NAME
axfer\-transfer \- transferrer of audio data frame for sound devices and nodes.

.SH SYNOPSIS

.B axfer transfer
.I direction
[
.I common\-options
] [
.I backend\-options
] [
.I filepath
]

.B axfer transfer
.I direction
[
.I common\-options
] [
.I backend\-options
]
.I \-I
|
.I \-\-separate\-channels filepath ...

direction =
.B capture
|
.B playback

common\-options = ( read
.I OPTIONS
section )

backend\-options = ( read
.I OPTIONS
section )

filepaths = ( read
.I OPTIONS
section )

.SH DESCRIPTION
The
.B transfer
subcommand of
.B axfer
performs transmission of audio data frames for devices available in supported
backends. This program is essentially designed to use alsa\-lib APIs
(libasound backend) to handle sound devices supported by Linux sound subsystem
(ALSA).

.SH OPTIONS

.SS Direction

.TP
.B capture
Operates for capture transmission.

.TP
.B playback
Operates for playback transmission.

.SS Filepath

Filepath is handled as a path relative to current working directory of run time
if it\(aqs not full path from root directory.

The standard input or output is used if filepath is not specified or given as
.I \(aq\-\(aq
\&.

For playback transmission, container format of given
\I filepath
is detected automatically and metadata is used for parameters of sample format,
channels, rate, duration. If nothing detected, content of given file path is
handled as raw data. In this case, the parameters should be indicated as
options.

Multiple
.I filepaths
are allowed with
.I \-I
|
.I \-\-separate\-channels
option. In this case, standard input and output is not available. The same
.I filepath
is not allowed except for paths listed below:
 \- /dev/null
 \- /dev/zero
 \- /dev/full
 \- /dev/random
 \- /dev/urandom

.SS Common options

.TP
.B \-h, \-\-help
Print help messages and finish run time. Not yet implemented.

.TP
.B \-q, \-\-quiet
Quiet mode. Suppress messages (not sound :))

.TP
.B \-v, \-\-verbose
Verbose mode. Runtime dumps supplemental information according to the number of
this option given in command line.

.TP
.B \-d, \-\-duration=#
Interrupt after # seconds. A value of zero means infinity. The default is zero,
so if this option is omitted then the transmission process will run until it is
killed. Either
.I \-d
or
.I \-s
option is available exclusively.

.TP
.B \-s, \-\-samples=#
Interrupt after transmission of # number of data frames. A value of zero means
infinity. The default is zero, so if this options is omitted then the
transmission process will run until it is killed. Either
.I \-d
or
.I \-s
option is available exclusively.

.TP
.B \-f, \-\-format=FORMAT
Indicate format of audio sample. This is required for capture transmission, or
playback transmission with files including raw audio data.

Available sample format is listed below:
 - [S8|U8|S16|U16|S32|U32][_LE|_BE]
 - [S24|U24][_LE|_BE]
 - FLOAT[_LE|_BE]
 - FLOAT64[_LE|_BE]
 - IEC958_SUBFRAME[_LE|_BE]
 - MU_LAW
 - A_LAW
 - [S20|U20][_LE|_BE]
 - [S24|U24][_3LE|_3BE]
 - [S20|U20][_3LE|_3BE]
 - [S18|U18][_3LE|_3BE]
 - DSD_U8
 - DSD_[U16|U32][_LE|_BE]

If endian\-ness is omitted, host endian\-ness is used.

Some special formats are available:
 - cd (16 bit little endian, 44100, stereo) [= \-f S16_LE \-c 2 \-r 44100]
 - cdr (16 bit big endian, 44100, stereo) [= \-f S16_BE \-c 2 \-f 44100]
 - dat (16 bit little endian, 48000, stereo) [= \-f S16_LE \-c 2 \-r 48000]

If omitted,
.I U8
is used as a default. Actual available formats are restricted by each
transmission backend.

Unavailable sample format is listed below. These format has size of data frame
unaligned to byte unit.

 - IMA_ADPCM
 - MPEG
 - GSM
 - SPECIAL
 - G723_24
 - G723_24_1B
 - G723_40
 - G723_40_1B

.TP
.B \-c, \-\-channels=#
Indicate the number of audio data samples per frame. This is required for
capture transmission, or playback transmission with files including raw audio
data. The value should be between
.I 1 to
.I 256
\&. If omitted,
.I 1
is used as a default.

.TP
.B \-r, \-\-rate=#
Indicate the number of audio data frame per second. This is required for
capture transmission, or playback transmission with files including raw audio
data. If the value is less than
.I 1000
, it\(aqs interpreted by
.I kHz
unit. The value should be between
.I 2000
and
.I 192000
\&. If omitted,
.I 8000
is used as a default.

.TP
.B \-t, \-\-file\-type=TYPES
Indicate the type of file. This is required for capture transmission. Available
types are listed below:
 - wav: Microsoft/IBM RIFF/Wave format
 - au, sparc: Sparc AU format
 - voc: Creative Tech. voice format
 - raw: raw data

When nothing is indicated, for capture transmission, the type is decided
according to suffix of
.I filepath
, and
.I raw
type is used for fallback.

.TP
.B \-I, \-\-separate\-channels
Indicate this option when several files are going to be handled. For capture
transmission, if one filepath is given as
.I filepath
, a list of
.I filepaths
is generated in a formula \(aq<filepath>\-<sequential number>[.suffix]\(aq.
The suffix is omitted when raw format of container is used.

.TP
.B \-\-dump\-hw\-params
Dump hardware parameters and finish run time if backend supports it.

.TP
.B \-\-xfer\-backend=BACKEND
Select backend of transmission from a list below. The default is libasound.
.br
 - libasound
 - libffado (optional if compiled)

.SS Backend options for libasound

(placeholder)

.SS Backend options for libffado

(placeholder)

.SH POSIX SIGNALS
During transmission,
.I SIGINT
and
.I SIGTERM
will close handled files and PCM substream to be going to finish run time.

.I SIGTSTP
will suspend PCM substream and
.I SIGCONT
will resume it. No XRUNs are expected.

The other signals perform default behaviours.

.SH EXAMPLES

.PP
.in +4n
.EX
.B $ axfer transfer playback \-d 1 something
.EE
.in
.PP

The above will transfer audio data frame in \(aqsomething\(aq file for playback
during 1 second.  The sample format is detected automatically as a result to
parse \(aqsomething\(aq as long as it\(aqs compliant to one of Microsoft/IBM
RIFF/Wave, Sparc AU, Creative Tech. voice formats. If nothing detected,
.I \-r
,
.I \-c
and
.I \-f
should be given,
or
.I \-f
should be given with special format.

.PP
.in +4n
.EX
.B $ axfer transfer playback \-r 22050 \-c 1 \-f S16_LE \-t raw something
.EE
.in
.PP

The above will transfer audio data frame in \(aqsomething\(aq file including no
information of sample format, as sample format of 22050 Hz, monaural, signed 16
bit little endian PCM for playback. The transmission continues till catching
.I SIGINT
from keyboard or
.I SIGTERM
by
.I kill(1)
\&.

.PP
.in +4n
.EX
.B $ axfer transfer capture \-d 10 \-f cd something.wav
.EE
.in
.PP

The above will transfer audio data frame to \(aqsomething.wav\(aq file as
sample format of 44.1 kHz, 2 channels, signed 16 bit little endian PCM, during
10 seconds. The file format is Microsoft/IBM RIFF/Wave according to suffix of
the given
.I filepath
\&.

.PP
.in +4n
.EX
.B $ axfer transfer capture \-s 1024 \-r 48000 \-c 2 \-f S32_BE \-I \-t au channels
.EE
.in
.PP

The above will transfer audio data frame as sample format of 48.0 kHz, 2
channels, signed 32 bit big endian PCM for 1,024 number of data frames to files
named \(aqchannels\-1.au\(aq and \(aqchannels\-2.au\(aq.

.SH COMPATIBILITY TO APLAY

The
.B transfer
subcommand of
.B axfer
is designed to keep compatibility to aplay(1). However some options below are
not compatible due to several technical reasons.

.TP
.I \-I, \-\-separate\-channels
This option is supported just for files to store audio data frames corresponding
to each channel. In aplay(1) implementation, this option has an additional
effect to use PCM buffer aligned to non\-interleaved order if a target device
supports. As of 2018, PCM buffer of non\-interleaved order is hardly used by
sound devices.

.TP
.I \-\-max\-file\-time=#
This option is unsupported. In aplay(1) implementation, the option has an
effect for capture transmission to save files up to the same number of data
frames as the given value by second unit, or the maximum number of data frames
supported by used file format. When reaching to the limitation, used file is
closed, then new file is opened and audio data frames are written. However, this
option requires extra handling of files and shall increase complexity of main
loop of axfer.

.TP
.I \-\-use\-strftime=FORMAT
This option is unsupported. In aplay(1) implementation, the option has an effect
for capture transmission to generate file paths according to given format in
which some extra formats are available as well as formats supported by
strftime(3). However, this option requires extra string processing for file
paths and it\(aqs bothersome if written in C language.

.TP
.I \-\-process\-id\-file=FILEPATH
This option is unsupported. In aplay(1) implementation, the option has an effect
to create a file for given value and write out process ID to it. This file
allows users to get process ID and send any POSIX signal to aplay process.
However, this idea has some troubles for file locking when multiple aplay
processes run with the same file.

.TP
.I \-V, \-\-vumeter=TYPE
This option is not supported at present. In aplay(1) implementation, this option
has an effect to occupy stdout with some terminal control characters and display
vumeter for monaural and stereo channels. However, some problems lay; this
feature is just for audio data frames with PCM format, this feature brings
disorder of terminal after aborting, stdout is not available for pipeline.

.TP
.I \-i, \-\-interactive
This option is not supported at present. In aplay(1) implementation, this option
has an effect to occupy stdin for key input and suspend/resume PCM substream
according to pushed enter key. However, this feature requires an additional
input handling in main loop and leave bothersome operation to maintain PCM
substream.

.TP
.I SIGTSTP, SIGCONT
This performs suspend/resume of PCM substream. In aplay(1) implementation,
these operations bring XRUN state to the substream, and suspend/resume is done
in interactive mode in the above. Some developers use the signal for recovery
test from XRUN. At present, no alternative is supported for the test.

.TP
.I SIGUSR1
This is not supported. In aplay(1) implementation, this signal is assigned to a
handler to close a current file to store audio data frame and open a new file
to continue processing. However, as well as
.I \-\-max\-file\-time
option, this option should increase complexity of main loop of axfer.

.SH DESIGN

.SS Modular structure

This program consists of three modules;
.I xfer
,
.I mapper
and
.I container
\&.
Each module has an abstraction layer to enable actual implementation.

.nf
           --------     ----------     -------------
device <-> | xfer | <-> | mapper | <-> | container | <-> file
           --------     ----------     -------------
            libasound    single         wav
            libffado     multiple       au
                                        voc
                                        raw
.fi

The
.I xfer
module performs actual transmission to devices and nodes. The module can have
several transmission backends. As a default backend,
.I libasound
backend is used to perform transmission via alsa\-lib APIs. The module allows
each backend to parse own command line options.

The
.I container
module performs to read/write audio data frame via descriptor for file/stream
of multimedia container or raw data. The module automatically detect type of
multimedia container and parse parameters in its metadata of data header. At
present, three types of multimedia containers are supported; Microsoft/IBM
RIFF/Wave (
.I wav
), Sparc AU (
.I au
) and Creative Technology voice (
.I voc
). Additionally, a special container is prepared for raw audio data (
.I raw
).

The
.I mapper
module handles buffer layout and alignment for transmission of audio data frame.
The module has two implementations;
.I single
and
.I multiple
\&.
The
.I single
backend uses one container to construct the buffer. The
.I multiple
backend uses several containers to construct it.

.SS Care of copying audio data frame

Between the
.I xfer
module and
.I mapper
module, a pointer to buffer including audio data frames is passed. This buffer
has two shapes for interleaved and non\-interleaved order. For the former, the
pointer points to one buffer. For the latter, the pointer points to an array in
which each element points to one buffer. Between the
.I mapper
module and
.I container
module, a pointer to one buffer is passed because supported media containers
including raw type store audio data frames in interleaved order.

In passing audio data frame between the modules, axfer is programmed to avoid
copying between a buffer to another buffer as much as possible. For example, in
some scenarios below, no copying occurs between modules.

 - xfer(mmap/interleaved), mapper(single), container(any)
 - xfer(mmap/non\-interleaved), mapper(multiple), containers(any)

.SH SEE ALSO
\fB
axfer(1),
axfer\-list(1),
alsamixer(1),
amixer(1)
\fP

.SH AUTHOR
Takashi Sakamoto <o\-takashi@sakamocchi.jp>