audioconvert(1) manual page
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audioconvert - convert audio file formats
audioconvert [
-pF ] [ -f outfmt ] [ -o outfile ] [ [ -i infmt ] [ file... ] ] ...
SUNWaudio
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 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.
- -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 filename is present, or if the special filename ‘-’ is specified, audio
data is read from the standard input.
- -?
- Help: Print a command line usage
message.
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
-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
-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 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) Specify
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.
Record voice data and compress it before storing it to
a file:
- example% audiorecord | audioconvert -f g721 > mydata.au
Concatenate
two Sun format audio files, regardless of their data format, and output
an 8-bit -law, 16 kHz, mono file:
- example% audioconvert -f ulaw,rate=16k,mono
-o outfile.au infile1 infile2
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
audioplay(1)
, audiorecord(1)
,
file(1)
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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