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 -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
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 out-
put 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:
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User Commands audioconvert(1)
-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 out-
put file. Defaults for unspecified fields are
derived from the input file format. Valid key-
words and values are listed in the next sec-
tion.
-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. Ordi-
narily, the input data format is derived from
the audio file header. This option is required
when converting audio data that is not pre-
ceded 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 follow-
ing that specification, until a new input for-
mat is specified.
file File Specification: The named audio files are
concatenated, converted to the output format,
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User Commands audioconvert(1)
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 CIT G.711 -law encoding. This is
an 8-bit format primarily used for
telephone quality speech.
alaw CIT G.711 A-law encoding. This is
an 8-bit format primarily used for
telephone quality speech in Europe.
linear8, Linear Pulse Code Modulation (PCM)
linear16, encoding. The name identifies the
linear32 number of bits of precision.
linear16 is typically used for high
quality audio data.
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User Commands audioconvert(1)
pcm Same as linear16.
g721 CIT 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 CIT 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 simi-
lar 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.
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User Commands audioconvert(1)
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 unrecog-
nized file header.
USAGE
See largefile(5) 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 stor-
ing 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
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
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User Commands audioconvert(1)
ATRIBUTE TYPE ATRIBUTE VALUE
Architecture SPARC, x86
Availability SUNWauda
Interface Stability Evolving
SEE ALSO
audioplay(1), audiorecord(1), file(1), attributes(5), large-
file(5)
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.
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