audioconvert - convert audio file formats
audioconvert [-pF] [-f outfmt] [-o outfile] [ [-i infmt]
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 -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 con-
catenated together. The output file will contain an audio
file header, unless format=raw is specified in the output
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 out-
put format. The existing files are then overwritten with the
The file(1) command decodes and prints the audio data format
of Sun audio files.
The following options are supported:
-p In Place: The input files are individually converted
to the format specified by the -f option and rewrit-
ten. If a target file is a symbolic link, the underly-
ing 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.
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
Output File: All input files are concatenated, con-
verted to the output format, and written to the named
output file. If -o and -p are not specified, the con-
catenated output is written to the standard output.
The -p option may not be specified with -o.
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 specifica-
tion syntax is the same as the -f output file format.
Multiple input formats may be specified. An input for-
mat describes all input files following that specifi-
cation, until a new input format is specified.
file File Specification: The named audio files are con-
catenated, 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.
The syntax for the input and output format specification is:
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). Stan-
dard of the commonly used sample rates are: 8k, 16k,
32k, 44.1k, and 48k.
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.
This option specifies the digital audio data represen-
tation. Encodings determine precision implicitly (ulaw
implies 8-bit precision) or explicitly as part of the
name (for example, linear16). Valid encoding values
ulaw CCITT G.711 -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.
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
-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
-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
dat Equivalent to
This option specifies the audio file format. Valid
sun Sun compatible file format (the default).
raw Use this format when reading or writing raw
audio data (with no audio header), or in con-
junction with an offset to import a foreign
audio file format.
(-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.
See largefile(5) for the description of the behavior of
audioconvert when encountering files greater than or equal
to 2 Gbyte ( 2**31 bytes).
Example 1: Recording and compressing voice data before stor-
Record voice data and compress it before storing it to a
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 attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Architecture | SPARC, x86 |
| Availability | SUNWauda |
| Interface Stability | Evolving |
audioplay(1), audiorecord(1), file(1), attributes(5), large-
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.
Man(1) output converted with