afSetLoopStart(3dm)afSetLoopStart(3dm)NAME
afSetLoopStart, afSetLoopEnd, afSetLoopMode, afSetLoopTrack - set the
start/end markers, play mode, and track in an AFfilehandle structure for
a specified loop.
SYNOPSIS
#include <dmedia/audiofile.h>
void afSetLoopStart(AFfilehandle file, int instid,
int loopid, int markid)
void afSetLoopEnd(AFfilehandle file, int instid,
int loopid, int markid)
void afSetLoopTrack(AFfilehandle file, int instid,
int loopid, int trackid)
void afSetLoopMode(AFfilehandle file, int instid,
int loopid, int mode)
PARAMETER
setup is an AFfilehandle structure, previously created by a call to
afOpenFile(3dm) or afOpenFD(3dm), which opened an audio file
for write access.
instid is a positive integer value which identifies a chunk of
instrument parameters. Since the number of supported inst
chunks varies with file format, applications should always
retrieve this value via afGetInstIDs(3dm).
loopid is a positive integer value which identifies a loop stored in
the instrument configuration given by instid.
markid is a positive integer marker value which identifies a marker
associated with the track given by trackid.
The start and end sample frames of a loop are indicated by
marker positions stored in marker structures.
trackid is a positive integer ID indicating which audio track in file
will contain the specified loop.
Since all currently supported audio file formats contain a
single audio track per file, the constant value
AF_DEFAULT_TRACK should always be used here for now.
mode is a constant integer indicates the play mode for the loop.
DESCRIPTION
These routines allow you to specify loops in an audio track. Each takes
a loopid argument which provides a handle to a loop structure.
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afSetLoopStart(3dm)afSetLoopStart(3dm)
In an AIFF-C (or AIFF) file, the instrument chunk, denoted by integer
constant AF_DEFAULT_INST, contains two loops - a "sustain" loop and a
"release" loop.
You can obtain loop ID's for the two loops by calling afGetLoopIDs(3dm)
after you've opened an audio file, or you can supply your own loop ID's
by calling afInitLoopIDs(3dm) before the file is opened.
For AIFF and AIFF-C files you map your loop ID list to the
sustain/release loops for the default instrument by calling
afSetInstParamLong(3dm).
The start and end sample frames for a loop are indicated by marker
structures. An AIFF-C (or AIFF) track may contain one or more marker
structures. A marker structure stores a location in an audio track.
To store two loops, you typically need four markers, two for each loop.
See the man page for afSetMarkPosition(3dm) for information about how you
assign a marker to a specific location in an audio track.
afSetLoopStart() set the start frame marker for a given loop in the
specified audio track. afSetLoopEnd sets the end frame marker for a
loop. The loop is specified by the value of loopid, a loop identifier
which was previously configured into the audio track by a call to
afInitLoopIDs().
afSetLoopTrack() is a placeholder routine which specifies an audio track
in a file for a loop. Since an AIFF-C (AIFF) file always contain one
audio track, the loops automatically map to AF_DEFAULT_TRACK.
afSetLoopMode() sets the play mode for a loop. The following modes are
supported:
AF_LOOP_MODE_NOLOOP causes the loop to be ignored
AF_LOOP_MODE_FORW forward loop
AF_LOOP_MODE_FORWBAKW forward/backward loop
NOTES
It is now possible to set the loop start and end frame directly without
using the associated markers (see afSetLoopStartFrame(3dm)). This is
useful and necessary for audio file formats which support loops which are
independent of any markers, and for formats which support loops but which
do not support markers at all. For formats which always associate loops
and markers, such as AIFF(4) and WAVE(4), afSetLoopStart() must be used
or the file update will fail.
SEE ALSOafNewFileSetup(3dm), afOpenFile(3dm), afInitLoopIDs(3dm),
afGetLoopIDs(3dm), afInitMarkIDs(3dm), afSetMarkPosition(3dm)
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