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.TH AUDIO 6
.SH NAME
audio \- Inferno audio file format
.SH DESCRIPTION
Inferno audio files accepted by commands such as
.IR auplay (1)
have a simple format.
The file contains a header consisting of
non-empty lines of text specifying the data format and characteristics,
followed by an empty line,
followed by the audio data in binary form.
The data can be copied
directly to a suitable audio device (see
.IR audio (3))
correctly configured,
using
.BR read ,
.B write
or
.B stream
(see
.IR sys-read (2)).
.PP
Each header line corresponds to a command that can be written to
the control file
.B audioctl
of the
.IR audio (3)
device.
The first line of the header must be a
.BR rate
command;
other commands can appear in any order.
The commands available are:
.TP
.BI rate " n"
The data was recorded at
.I n
Hz, typically one of
.BR 44100 ,
.BR 22050 ,
.BR 11025
or
.BR 8000
but other values are legal.
.TP
.BI chans " n"
There are
.I n
channels of audio data (eg, 1 for mono and 2 for stereo).
.TP
.BI bits " n"
Each sample is
.I n
bits (typically 8 or 16).
.TP
.BI enc " e"
.br
The string
.I e
gives the recording format, and
will usually be one of the following:
.BR ulaw ,
.BR alaw ,
.BR pcm
or
.BR adpcm .
.PP
The audio data is stored with a sample from each channel in turn
(`left' sample first if stereo, regardless of encoding or data size).
Data encoded as
.B pcm
is little-endian, 2's complement if 16-bit, but unsigned if 8 bit.
The
.B adpcm
encoding uses 4-bit samples (two mono samples or one stereo sample per byte, again little-endian).
.SH SEE ALSO
.IR auplay (1),
.IR audio (3)
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