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NAME
     audio_filehdr,    audio_isaudiofile,     audio_read_filehdr,
     audio_decode_filehdr,                   audio_write_filehdr,
     audio_rewrite_filesize - audio file header manipulation

SYNOPSIS
     #include <multimedia/libaudio.h>

     int audio_isaudiofile(char * name);

     int audio_read_filehdr(int  fd ,
     Audio_hdr *hp,
     char *infop,
     unsigned ilen);

     int audio_decode_filehdr(unsigned char *buf,
     Audio_hdr *hp,
     unsigned *ilenp);

     int audio_write_filehdr(int fd,
     Audio_hdr *hp,
     char *infop,
     unsigned ilen);

     int audio_rewrite_filesize(int fd,
     unsigned size);

DESCRIPTION
     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 Audio_hdr structure used by many of  the  libaudio  rou-
     tines for describing audio data is not an exact duplicate of
     the audio file header.  Several  routines  are  provided  to
     read  and  write  file  headers so that programs need not be
     concerned with the details of the exact file  header  struc-
     ture.

     audio_isaudiofile() returns TRUE if the named  file  appears
     to be an audio file, FALSE otherwise.  Note that only a lim-
     ited degree of file  header  consistency  checking  is  per-
     formed.   The  audio_read_filehdr() routine is somewhat more
     comprehensive in its tests.  However, audio_isaudiofile() is
     often  sufficient  to  determine whether or not a particular
     file is of any interest to an application.

     audio_read_filehdr() reads an audio  file  header  from  the
     given  input  stream, decoding its fields into the Audio_hdr
     structure whose address is given by hp.  If successful,  the
     value  AUDIO_SUCCESS  is returned and the current file posi-
     tion of the stream is updated to refer to the  beginning  of
     the audio data.

     The data_size field of the returned Audio_hdr  structure  is
     set  to  the  length,  in bytes, of the audio data.  If this
     length is indeterminate (for instance, if the data is  being
     read   from  a  pipe),  this  field  is  set  to  the  value
     AUDIO_UNKNOWN_SIZE.

     Note that the input file descriptor must not  be  set  to  a
     non-blocking I/O mode.  If non-blocking behavior is desired,
     it should be enabled after this routine returns.

     The infop argument, if not NULL, specifies the address of  a
     buffer, whose size is given by ilen, into which the informa-
     tion field of the audio  file  is  copied.   The  buffer  is
     always  returned  NULL-terminated,  even if it was not large
     enough to hold the entire file information field.

     audio_decode_filehdr() decodes a buffer presumed to  contain
     an  audio  file  header.   Though  ordinarily called only by
     audio_read_filehdr(), this routine  may  be  used  in  cases
     where  an  application wishes to read the information struc-
     ture itself.  The buf argument specifies the address of  the
     file  header  information  to be decoded.  The length of the
     information field is returned at the address  given  by  the
     ilenp argument.

     audio_write_filehdr() encodes the given Audio_hdr  structure
     into an audio file header and writes it to the output stream
     denoted by the fd argument.  If the infop  argument  is  not
     NULL,  it  specifies the address of a buffer containing ilen
     bytes of file information that will be  written  immediately
     following  the  file  header.   The information structure is
     always zero-padded so  that  the  audio  data  begins  on  a
     double-word  boundary.  Note that the output file descriptor
     must not have been set to a non-blocking I/O mode.

     audio_rewrite_filesize() attempts to rewrite the audio  file
     header of the file specified by the fd argument, setting the
     data length to size.  If successful, the value AUDIO_SUCCESS
     is  returned.  If the specified file descriptor is incapable
     of backward seeks (for example, if it  refers  to  a  pipe),
     AUDIO_ERR_NOEFFECT is returned.

RETURN VALUES
     With the exception of  audio_isaudiofile(),  these  routines
     return  AUDIO_SUCCESS on successful completion or, if unsuc-
     cessful, one of the following error codes:

     AUDIO_UNIXERROR          An error occurred while executing a
                              system  library function.  The glo-
                              bal value errno contains the  error
                              code.

     AUDIO_ERR_BADHDR         The user-supplied Audio_hdr  struc-
                              ture  contains  an inconsistency or
                              invalid value.

     AUDIO_ERR_BADFILEHDR     The audio file header  contains  an
                              inconsistency.

     AUDIO_ERR_NOEFFECT       The requested operation  could  not
                              be performed.

SEE ALSO
     audio_intro(3), audio_hdr(3)

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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