afGetPCMMapping(3dm)					  afGetPCMMapping(3dm)

NAME    [Toc]    [Back]

     afGetPCMMapping, afGetVirtualPCMMapping - get the track / virtual PCM
     mapping values for	a specified audio track	from an	AFfilehandle structure

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/audiofile.h>

     void afGetPCMMapping(AFfilehandle file, int track,
				 double	*slope,	double *intercept,
				 double	*minclip, double *maxclip)

     void afGetVirtualPCMMapping(AFfilehandle file, int	track,
				 double	*slope,	double *intercept,
				 double	*minclip, double *maxclip)

PARAMETER    [Toc]    [Back]

     file    is	an AFfilehandle	structure, previously created by a call	to
	     afOpenFile(3dm).

     track   is	an integer which identifies an audio track in file.

	     Since all currently supported file	formats	contain	exactly	one
	     audio track per file, the constant	AF_DEFAULT_TRACK should	always
	     be	used here for now.

     slope   is	a pointer to a double precision	floating point value which
	     specifies the amplitude scaling factor for	the audio waveform
	     associated	with track

     intercept
	     is	a pointer to a double precision	floating point value which
	     specifies the audio waveform vertical midpoint (zero-crossing)
	     value associated with track

     minclip is	a pointer to a double precision	floating point value
	     indicating	the minimum or most negative audio data	sample value
	     that will be returned.  Any value less than this is set to
	     minclip

     maxclip is	a pointer to a double precision	floating point value
	     indicating	the maximum or most positive audio data	sample value
	     to	be returned.  Any value	greater	than this is set to maxclip

DESCRIPTION    [Toc]    [Back]

     afGetPCMMapping() returns the four	values associated with the PCM (Pulse
     Code Modulation) mapping in an audio track	in the file represented	by the
     AFfilehandle argument, using the double pointer arguments.

     afGetVirtualPCMMapping() does the same for	the virtual format for the
     given track, as set by any	combination of calls to
     afSetVirtualPCMMappingPage 1






afGetPCMMapping(3dm)					  afGetPCMMapping(3dm)



     See afIntro(3dm) for a detailed description of the	PCM mapping technique.

CAVEATS    [Toc]    [Back]

     PCM mapping is only useful	for modifying frames as	they are read into or
     written out from a	buffer via afReadFrames(3dm) or	afWriteFrames(3dm).
     None of the currently supported file formats have the capability to store
     this information, even though the actual mapping can and will be applied
     to	the frames stored in those files.  Therefor, it	is important to	be
     careful what values you specify.  In general, all two's complement	and
     floating point sample formats are expected	to be symmetrical about	zero,
     i.e., the intercept will be 0.0 and minclip and maxclip will be negative
     and positive N, where N is	some non-zero positive value.

SEE ALSO    [Toc]    [Back]

     afWriteFrames(3dm), afReadFrames(3dm), afInitPCMMapping(3dm),
     afSetVirtualPCMMapping(3dm)


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