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NAME
     audio_intro, libaudio.a - audio library functions

SYNOPSIS
     #include <multimedia/libaudio.h>

DESCRIPTION
     libaudio.a provides a preliminary interface to many  of  the
     common  operations  necessary to access and manipulate audio
     files and devices.  By embodying the specifics of file  for-
     mats and device ioctl commands in library routines, programs
     may be insulated, in part, from future changes to the inter-
     face and data storage formats.

File Header
     Audio files contain a header that has a magic number  (iden-
     tifying  the file as an audio file) and fields that describe
     the encoding format used to store the audio  data.   Immedi-
     ately  following the header is a variable-length information
     field in  which,  for  instance,  ASCII  annotation  may  be
     stored.

     The format of the audio file header  is  compatible  with  a
     subset  of  the  NeXT  sound  file  header.  Sun has adopted
     NeXT's sound file header ideas to facilitate the transparent
     sharing  of  audio  files  in a networked environment.  (The
     NeXT Nested and Indirect sound file types are not  currently
     supported.)

     In order that audio files may be successfully shared amongst
     multiple  machine  architectures, the header and data fields
     are written using  big-endian  byte-ordering.   Though  this
     means  that byte-swapping may be necessary to read and write
     some data encodings on little-endian machines  such  as  the
     Sun386i,  this  overhead is largely overwhelmed by all other
     signal manipulation operations.  The benefits of transparent
     file access far outweigh the costs.

     Routines to support the reading and writing  of  audio  file
     headers  are documented in the audio_filehdr(3) manual page.
     These routines convert between the file header  format  used
     for  file  interchange  and  the in-core audio header format
     used by most audio applications.

Audio Header
     Audio data is described by an Audio_hdr  structure  that  is
     similar,  but  not identical, to the audio file header.  The
     audio header structure  is  described  in  the  audio_hdr(3)
     manual  page.   The audio_misc(3) manual page describes rou-
     tines that perform some simple transformations based on  the
     contents of the audio header structure.

Audio Device Control
     The audio(4) manual page describes the direct  interface  to
     the  audio  i/o  device  (/dev/audio)  and the audio control
     pseudo-device (/dev/audioctl).  For the most part,  however,
     programs   may   use   the   routines   documented   in  the
     audio_device(3) manual page to access and control  the  dev-
     ice.

Audio Data Conversions
     The SPARCstation audio device operates on data that has been
     encoded  in  u-law  format, a quasi-logarithmic compression.
     Since most signal-processing algorithms  perform  arithmetic
     on  linearly  encoded  data,  it is convenient to be able to
     convert to  and  from  a  linear  PCM  representation.   The
     audio_ulaw2linear(3)  manual page describes macros that will
     perform these transformations.

SEE ALSO
     audio_convert(3),      audio_filehdr(3),       audio_hdr(3),
     audio_misc(3), audio_ulaw2linear(3), audio(4)

NOTES
     NeXT is a trademark of NeXT, Inc.

FUTURE DIRECTIONS
     Although access to audio file headers are  partly  concealed
     in the file header routines, the data formats themselves are
     not properly hidden.  Routines  to  demultiplex  interleaved
     audio  channels,  and  to transparently convert between data
     encodings, should be provided.

     Access to many of the audio device status and control fields
     has  been  concealed in the audio device routines.  As audio
     server  technology  emerges,  these  interfaces  may  remain
     stable  while  the  underlying implementation changes.  How-
     ever, access to the data streams of the audio device  should
     be similarly concealed.

WARNINGS
     The manual pages, header files, and object  library  associ-
     ated  with /usr/demo/SOUND/libaudio.a are furnished on an as
     is basis as a preliminary interface to several useful  audio
     data-processing  capabilities.   A  future  release  of  the
     operating system may redefine the  syntax  or  semantics  of
     some of the functions described herein.

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