next(4)                                                                next(4)


NAME
     next, au, sun - NeXT / Sun .au Audio File Formats

SYNOPSIS
     #include <dmedia/audiofile.h>

DESCRIPTION
     The Audio File Library currently supports 13 of the commonly found audio
     file formats, i.e., is able to recognize, read, and write sample data and
     header information to and from files in these formats.  It is important
     not to confuse sample or audio data formats with file formats.  The
     former refers to the bit-wise organization of the sound samples in the
     file, i.e., whether the format is 8-bit integer or 16-bit unsigned, etc.
     Audio file format refers to the structure of the audio file header, the
     chunk of on-disk data which preceeds the samples and which provides
     information about the file to the audio program.  A single audio file
     format may support a large variety of sample formats.

     The NeXT File Format (next) was created by NeXT, Inc.  It consists of a
     fixed-length header of 24 bytes followed by a variable-length text or
     data block (minimum length 4 bytes), followed by a contiguous block of
     binary data representing the sound samples.  Sun Microsystems, Inc., used
     this format as the model for their .au file format (but see CAVEATS
     below).

DATA FORMAT SPECIFICATIONS
     Sample Formats:
          Two's complement integer, 32-bit single-precision floating point, or
          64-bit double-precision floating point

     Sample Widths:
          For integer:  8, 16, 24, and 32 bit;  floating points are always 32
          and 64 bit, respectively

     Byte Orders:
          Only bigendian supported;  littleendian files are generated on Intel
          NeXT machines

     Channel Counts:
          Any nonzero number, but 1, 2, and 4 are only ones found.

     Compression Formats:
          CCITT G.711 A-Law

          CCITT G.711 ulaw

          CCITT G.722 (SND_FORMAT_ADPCM_G722)

FILE FORMAT SPECIFICATIONS
     NeXT files can contain additional chunks of data.  Most of these are
     parsed by the AF and made available:


     Instrument Configurations:
          None allowed

     Markers:
          None allowed

     Miscellaneous Chunks:
              AF_MISC_NeXT    NeXT 'info' chunk

CAVEATS
     The AF_MISC_NeXT miscellaneous chunk is typically used to store a
     variable (and infinitely extendible) text string containing comments,
     copyright information, etc.  There are, however, a significant number of
     NeXT format soundfiles which use this space to store application-specific
     binary (i.e., non-ascii) data.  There is no guarenteed way to determine
     which is true, so applications should excercise care in printing the
     contents of this chunk.

     Most audio file format documents claim that NeXT and Sun .au files have
     identical header formats.  This is not the case.  The difference lies in
     the text block which follows the header:  NeXT files require that this
     chunk be at least 4 bytes (chars) long, whereas this chunk may be zero-
     length in a Sun .au file.

     The Audio File Library will always save 8kHz sampling rate values as the
     "SND_RATE_CODEC" value (8012.8210513).  The data in the file will not be
     rate-converted; the mapping only occurs in the header writing procedure.

SEE ALSO
     afInitFileFormat(3dm), afGetFileFormat(3dm), afIntro(3dm),
     afInitCompression(3dm), afGetCompression(3dm)


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