AUDIOCONVERT(1) User Commands AUDIOCONVERT(1)

NAME

audioconvert - convert audio file formats

SYNOPSIS

audioconvert [-pF] [-f outfmt] [-o outfile]
[ [-i infmt] [file]...] ...

DESCRIPTION

audioconvert converts audio data between a set of supported audio
encodings and file formats. It can be used to compress and decompress
audio data, to add audio file headers to raw audio data files, and to
convert between standard data encodings, such as u-law and linear
PCM.


If no filenames are present, audioconvert reads the data from the
standard input stream and writes an audio file to the standard
output. Otherwise, input files are processed in order, concatenated,
and written to the output file.


Input files are expected to contain audio file headers that identify
the audio data format. If the audio data does not contain a
recognizable header, the format must be specified with the -i option,
using the rate, encoding, and channels keywords to identify the input
data format.


The output file format is derived by updating the format of the first
input file with the format options in the -f specification. If -p is
not specified, all subsequent input files are converted to this
resulting format and concatenated together. The output file will
contain an audio file header, unless format=raw is specified in the
output format options.


Input files may be converted in place by using the -p option. When -p
is in effect, the format of each input file is modified according to
the -f option to determine the output format. The existing files are
then overwritten with the converted data.


The file(1) command decodes and prints the audio data format of Sun
audio files.

OPTIONS

The following options are supported:

-p
In Place: The input files are individually converted to
the format specified by the -f option and rewritten. If
a target file is a symbolic link, the underlying file
will be rewritten. The -o option may not be specified
with -p.


-F
Force: This option forces audioconvert to ignore any
file header for input files whose format is specified
by the -i option. If -F is not specified, audioconvert
ignores the -i option for input files that contain
valid audio file headers.


-f outfmt
Output Format: This option is used to specify the file
format and data encoding of the output file. Defaults
for unspecified fields are derived from the input file
format. Valid keywords and values are listed in the
next section.


-o outfile
Output File: All input files are concatenated,
converted to the output format, and written to the
named output file. If -o and -p are not specified, the
concatenated output is written to the standard output.
The -p option may not be specified with -o.


-i infmt
Input Format: This option is used to specify the data
encoding of raw input files. Ordinarily, the input data
format is derived from the audio file header. This
option is required when converting audio data that is
not preceded by a valid audio file header. If -i is
specified for an input file that contains an audio file
header, the input format string will be ignored, unless
-F is present. The format specification syntax is the
same as the -f output file format.

Multiple input formats may be specified. An input
format describes all input files following that
specification, until a new input format is specified.


file
File Specification: The named audio files are
concatenated, converted to the output format, and
written out. If no file name is present, or if the
special file name `-' is specified, audio data is read
from the standard input.


-?
Help: Prints a command line usage message.

Format Specification

The syntax for the input and output format specification is:


keyword=value[,keyword=value ...]


with no intervening whitespace. Unambiguous values may be used
without the preceding keyword=.

rate
The audio sampling rate is specified in samples per
second. If a number is followed by the letter k, it is
multiplied by 1000 (for example, 44.1k = 44100). Standard
of the commonly used sample rates are: 8k, 16k, 32k,
44.1k, and 48k.


channels
The number of interleaved channels is specified as an
integer. The words mono and stereo may also be used to
specify one and two channel data, respectively.


encoding
This option specifies the digital audio data
representation. Encodings determine precision implicitly
(ulaw implies 8-bit precision) or explicitly as part of
the name (for example, linear16). Valid encoding values
are:

ulaw
CCITT G.711 u-law encoding. This is an 8-bit
format primarily used for telephone quality
speech.


alaw
CCITT G.711 A-law encoding. This is an 8-bit
format primarily used for telephone quality
speech in Europe.


linear8,
linear16,
linear32
Linear Pulse Code Modulation (PCM) encoding.
The name identifies the number of bits of
precision. linear16 is typically used for
high quality audio data.


pcm
Same as linear16.


g721
CCITT G.721 compression format. This
encoding uses Adaptive Delta Pulse Code
Modulation (ADPCM) with 4-bit precision. It
is primarily used for compressing u-law
voice data (achieving a 2:1 compression
ratio).


g723
CCITT G.723 compression format. This
encoding uses Adaptive Delta Pulse Code
Modulation (ADPCM) with 3-bit precision. It
is primarily used for compressing u-law
voice data (achieving an 8:3 compression
ratio). The audio quality is similar to
G.721, but may result in lower quality when
used for non-speech data.

The following encoding values are also accepted as
shorthand to set the sample rate, channels, and encoding:

voice
Equivalent to
encoding=ulaw,rate=8k,channels=mono.


cd
Equivalent to
encoding=linear16,rate=44.1k,channels=stereo.


dat
Equivalent to
encoding=linear16,rate=48k,channels=stereo.


format
This option specifies the audio file format. Valid
formats are:

sun
Sun compatible file format (the default).


raw
Use this format when reading or writing raw audio
data (with no audio header), or in conjunction
with an offset to import a foreign audio file
format.


offset
(-i only) Specifies a byte offset to locate the start of
the audio data. This option may be used to import audio
data that contains an unrecognized file header.

USAGE

See largefile(7) for the description of the behavior of audioconvert
when encountering files greater than or equal to 2 Gbyte (2^31
bytes).

EXAMPLES

Example 1: Recording and compressing voice data before storing it

Record voice data and compress it before storing it to a file:


example% audiorecord | audioconvert -f g721 > mydata.au

Example 2: Concatenating two audio files

Concatenate two Sun format audio files, regardless of their data
format, and output an 8-bit ulaw, 16 kHz, mono file:


example% audioconvert -f ulaw,rate=16k,mono -o outfile.au infile1 infile2

Example 3: Converting a directory to Sun format

Convert a directory containing raw voice data files, in place, to Sun
format (adds a file header to each file):


example% audioconvert -p -i voice -f sun *.au

SEE ALSO

audioplay(1), audiorecord(1), file(1), largefile(7)

NOTES

The algorithm used for converting multi-channel data to mono is
implemented by simply summing the channels together. If the input
data is perfectly in phase (as would be the case if a mono file is
converted to stereo and back to mono), the resulting data may contain
some distortion.

February 8, 2020 AUDIOCONVERT(1)