audioconvert(1) User Commands audioconvert(1)
audioconvert - convert audio file formats
audioconvert [-pF] [-f outfmt] [-o outfile]
[ [-i infmt] [file]...] ...
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 recogniz-
able header, the format must be specified with the -i option, using the rate, encoding, and channels keywords to identify the input data
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.
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
-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.
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). 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 pre-
cision) or explicitly as part of the name (for example, linear16). Valid encoding values are:
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.
linear8, Linear Pulse Code Modulation (PCM) encoding. The name identifies the number of bits of precision. linear16 is typ-
linear16, ically 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 preci-
sion. 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 preci-
sion. 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 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 con-
tains 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
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 attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Architecture |SPARC, x86 |
|Availability |SUNWauda |
|Interface Stability |Evolving |
audioplay(1), audiorecord(1), file(1), attributes(5), largefile(5)
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 dis-
SunOS 5.11 16 Feb 2001 audioconvert(1)