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NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/audiofile.h>

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

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




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     Instrument	Configurations:
	  None allowed

     Markers:
	  None allowed

     Miscellaneous Chunks:
	      AF_MISC_NeXT    NeXT 'info' chunk

CAVEATS    [Toc]    [Back]

     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 zerolength
 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    [Toc]    [Back]

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


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