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6 .TH AUDIOCONVERT 1 "Feb 16, 2001"
7 .SH NAME
8 audioconvert \- convert audio file formats
9 .SH SYNOPSIS
10 .LP
11 .nf
12 \fBaudioconvert\fR [\fB-pF\fR] [\fB-f\fR \fIoutfmt\fR] [\fB-o\fR \fIoutfile\fR]
13 [ [\fB-i\fR \fIinfmt\fR] [\fIfile\fR]...] ...
14 .fi
16 .SH DESCRIPTION
17 .sp
18 .LP
19 \fBaudioconvert\fR converts audio data between a set of supported audio
20 encodings and file formats. It can be used to compress and decompress audio
21 data, to add audio file headers to raw audio data files, and to convert between
22 standard data encodings, such as -law and linear PCM.
23 .sp
24 .LP
25 If no filenames are present, \fBaudioconvert\fR reads the data from the
26 standard input stream and writes an audio file to the standard output.
27 Otherwise, input files are processed in order, concatenated, and written to the
28 output file.
29 .sp
30 .LP
31 Input files are expected to contain audio file headers that identify the audio
32 data format. If the audio data does not contain a recognizable header, the
33 format must be specified with the \fB-i\fR option, using the \fBrate\fR,
34 \fBencoding\fR, and \fBchannels\fR keywords to identify the input data format.
35 .sp
36 .LP
37 The output file format is derived by updating the format of the first input
38 file with the format options in the \fB-f\fR specification. If \fB-p\fR is not
39 specified, all subsequent input files are converted to this resulting format
40 and concatenated together. The output file will contain an audio file header,
41 unless \fBformat\fR=\fIraw\fR is specified in the output format options.
42 .sp
43 .LP
44 Input files may be converted in place by using the \fB-p\fR option. When
45 \fB-p\fR is in effect, the format of each input file is modified according to
46 the \fB-f\fR option to determine the output format. The existing files are then
47 overwritten with the converted data.
48 .sp
49 .LP
50 The \fBfile\fR(1) command decodes and prints the audio data format of Sun audio
51 files.
52 .SH OPTIONS
53 .sp
54 .LP
55 The following options are supported:
56 .sp
57 .ne 2
58 .na
59 \fB\fB-p\fR\fR
60 .ad
61 .RS 14n
62 \fIIn Place\fR: The input files are individually converted to the format
63 specified by the \fB-f\fR option and rewritten. If a target file is a symbolic
64 link, the underlying file will be rewritten. The \fB-o\fR option may not be
65 specified with \fB-p\fR.
66 .RE
68 .sp
69 .ne 2
70 .na
71 \fB\fB-F\fR\fR
72 .ad
73 .RS 14n
74 \fIForce\fR: This option forces \fBaudioconvert\fR to ignore any file header
75 for input files whose format is specified by the \fB-i\fR option. If \fB-F\fR
76 is not specified, \fBaudioconvert\fR ignores the \fB-i\fR option for input
77 files that contain valid audio file headers.
78 .RE
80 .sp
81 .ne 2
82 .na
83 \fB\fB-f\fR \fIoutfmt\fR\fR
84 .ad
85 .RS 14n
86 \fIOutput Format\fR: This option is used to specify the file format and data
87 encoding of the output file. Defaults for unspecified fields are derived from
88 the input file format. Valid keywords and values are listed in the next
89 section.
90 .RE
92 .sp
93 .ne 2
94 .na
95 \fB\fB-o\fR \fIoutfile\fR\fR
96 .ad
97 .RS 14n
98 \fIOutput File\fR: All input files are concatenated, converted to the output
99 format, and written to the named output file. If \fB-o\fR and \fB-p\fR are not
100 specified, the concatenated output is written to the standard output. The
101 \fB-p\fR option may not be specified with \fB-o\fR.
102 .RE
104 .sp
105 .ne 2
106 .na
107 \fB\fB-i\fR \fIinfmt\fR\fR
108 .ad
109 .RS 14n
110 \fIInput Format\fR: This option is used to specify the data encoding of raw
111 input files. Ordinarily, the input data format is derived from the audio file
112 header. This option is required when converting audio data that is not preceded
113 by a valid audio file header. If \fB-i\fR is specified for an input file that
114 contains an audio file header, the input format string will be ignored, unless
115 \fB-F\fR is present. The format specification syntax is the same as the
116 \fB-f\fR output file format.
117 .sp
118 Multiple input formats may be specified. An input format describes all input
119 files following that specification, until a new input format is specified.
120 .RE
122 .sp
123 .ne 2
124 .na
125 \fB\fIfile\fR\fR
126 .ad
127 .RS 14n
128 \fIFile Specification\fR: The named audio files are concatenated, converted to
129 the output format, and written out. If no file name is present, or if the
130 special file name `\(mi' is specified, audio data is read from the standard
131 input.
132 .RE
134 .sp
135 .ne 2
136 .na
137 \fB\fB-?\fR\fR
138 .ad
139 .RS 14n
140 \fIHelp\fR: Prints a command line usage message.
141 .RE
143 .SS "Format Specification"
144 .sp
145 .LP
146 The syntax for the input and output format specification is:
147 .sp
148 .LP
149 \fIkeyword\fR=\fIvalue\fR[,\fIkeyword\fR=\fIvalue\fR \|.\|.\|.\|]
150 .sp
151 .LP
152 with no intervening whitespace. Unambiguous values may be used without the
153 preceding \fIkeyword\fR=.
154 .sp
155 .ne 2
156 .na
157 \fB\fBrate\fR\fR
158 .ad
159 .RS 12n
160 The audio sampling rate is specified in samples per second. If a number is
161 followed by the letter \fBk\fR, it is multiplied by 1000 (for example, 44.1k =
162 44100). Standard of the commonly used sample rates are: 8k, 16k, 32k, 44.1k,
163 and 48k.
164 .RE
166 .sp
167 .ne 2
168 .na
169 \fB\fBchannels\fR\fR
170 .ad
171 .RS 12n
172 The number of interleaved channels is specified as an integer. The words
173 \fBmono\fR and \fBstereo\fR may also be used to specify one and two channel
174 data, respectively.
175 .RE
177 .sp
178 .ne 2
179 .na
180 \fB\fBencoding\fR\fR
181 .ad
182 .RS 12n
183 This option specifies the digital audio data representation. Encodings
184 determine precision implicitly (\fBulaw\fR implies 8-bit precision) or
185 explicitly as part of the name (for example, \fBlinear16\fR). Valid encoding
186 values are:
187 .sp
188 .ne 2
189 .na
190 \fB\fBulaw\fR\fR
191 .ad
192 .RS 13n
193 \fBCCITT G.711\fR -law encoding. This is an 8-bit format primarily used for
194 telephone quality speech.
195 .RE
197 .sp
198 .ne 2
199 .na
200 \fB\fBalaw\fR\fR
201 .ad
202 .RS 13n
203 \fBCCITT G.711\fR A-law encoding. This is an 8-bit format primarily used for
204 telephone quality speech in Europe.
205 .RE
207 .sp
208 .ne 2
209 .na
210 \fB\fBlinear8\fR,\fR
211 .ad
212 .br
213 .na
214 \fB\fBlinear16\fR,\fR
215 .ad
216 .br
217 .na
218 \fB\fBlinear32\fR\fR
219 .ad
220 .RS 13n
221 Linear Pulse Code Modulation (PCM) encoding. The name identifies the number of
222 bits of precision. \fBlinear16\fR is typically used for high quality audio
223 data.
224 .RE
226 .sp
227 .ne 2
228 .na
229 \fB\fBpcm\fR\fR
230 .ad
231 .RS 13n
232 Same as \fBlinear16\fR.
233 .RE
235 .sp
236 .ne 2
237 .na
238 \fB\fBg721\fR\fR
239 .ad
240 .RS 13n
241 \fBCCITT G.721\fR compression format. This encoding uses Adaptive Delta Pulse
242 Code Modulation (ADPCM) with 4-bit precision. It is primarily used for
243 compressing -law voice data (achieving a 2:1 compression ratio).
244 .RE
246 .sp
247 .ne 2
248 .na
249 \fB\fBg723\fR\fR
250 .ad
251 .RS 13n
252 \fBCCITT G.723\fR compression format. This encoding uses Adaptive Delta Pulse
253 Code Modulation (ADPCM) with 3-bit precision. It is primarily used for
254 compressing -law voice data (achieving an 8:3 compression ratio). The audio
255 quality is similar to \fBG.721,\fR but may result in lower quality when used
256 for non-speech data.
257 .RE
259 The following encoding values are also accepted as shorthand to set the sample
260 rate, channels, and encoding:
261 .sp
262 .ne 2
263 .na
264 \fB\fBvoice\fR\fR
265 .ad
266 .RS 9n
267 Equivalent to \fBencoding=ulaw,rate=8k,channels=mono\fR.
268 .RE
270 .sp
271 .ne 2
272 .na
273 \fB\fBcd\fR\fR
274 .ad
275 .RS 9n
276 Equivalent to \fBencoding=linear16,rate=44.1k,channels=stereo\fR.
277 .RE
279 .sp
280 .ne 2
281 .na
282 \fB\fBdat\fR\fR
283 .ad
284 .RS 9n
285 Equivalent to \fBencoding=linear16,rate=48k,channels=stereo\fR.
286 .RE
288 .RE
290 .sp
291 .ne 2
292 .na
293 \fB\fBformat\fR\fR
294 .ad
295 .RS 12n
296 This option specifies the audio file format. Valid formats are:
297 .sp
298 .ne 2
299 .na
300 \fB\fBsun\fR\fR
301 .ad
302 .RS 7n
303 Sun compatible file format (the default).
304 .RE
306 .sp
307 .ne 2
308 .na
309 \fB\fBraw\fR\fR
310 .ad
311 .RS 7n
312 Use this format when reading or writing raw audio data (with no audio header),
313 or in conjunction with an \fBoffset\fR to import a foreign audio file format.
314 .RE
316 .RE
318 .sp
319 .ne 2
320 .na
321 \fB\fBoffset\fR\fR
322 .ad
323 .RS 12n
324 (\fB-i\fR \fIonly\fR) Specifies a byte offset to locate the start of the audio
325 data. This option may be used to import audio data that contains an
326 unrecognized file header.
327 .RE
329 .SH EXAMPLES
330 .LP
331 \fBExample 1 \fRRecording and compressing voice data before storing it
332 .sp
333 .LP
334 Record voice data and compress it before storing it to a file:
336 .sp
337 .in +2
338 .nf
339 example% \fBaudiorecord | audioconvert -f g721 > mydata.au\fR
340 .fi
341 .in -2
342 .sp
344 .LP
345 \fBExample 2 \fRConcatenating two audio files
346 .sp
347 .LP
348 Concatenate two Sun format audio files, regardless of their data format, and
349 output an 8-bit ulaw, 16 kHz, mono file:
351 .sp
352 .in +2
353 .nf
354 example% \fBaudioconvert -f ulaw,rate=16k,mono -o outfile.au infile1 infile2\fR
355 .fi
356 .in -2
357 .sp
359 .LP
360 \fBExample 3 \fRConverting a directory to Sun format
361 .sp
362 .LP
363 Convert a directory containing raw voice data files, in place, to Sun format
364 (adds a file header to each file):
366 .sp
367 .in +2
368 .nf
369 example% \fBaudioconvert -p -i voice -f sun *.au\fR
370 .fi
371 .in -2
372 .sp
374 .SH ATTRIBUTES
375 .sp
376 .LP
377 See \fBattributes\fR(5) for descriptions of the following attributes:
378 .sp
380 .sp
381 .TS
382 box;
383 c | c
384 l | l .
385 ATTRIBUTE TYPE ATTRIBUTE VALUE
386 _
387 Architecture SPARC, x86
388 _
389 Interface Stability Evolving
390 .TE
392 .SH SEE ALSO
393 .sp
394 .LP
395 \fBaudioplay\fR(1), \fBaudiorecord\fR(1), \fBfile\fR(1), \fBattributes\fR(5)
396 .SH NOTES
397 .sp
398 .LP
399 The algorithm used for converting multi-channel data to mono is implemented by
400 simply summing the channels together. If the input data is perfectly in phase
401 (as would be the case if a mono file is converted to stereo and back to mono),
402 the resulting data may contain some distortion.