Marker Chunk

The Marker Chunk contains markers that point to positions in the sound data. Markers can be used for whatever purposes an application desires. The Instrument Chunk, defined later in this document, uses markers to mark loop beginning and end points, for example.

Markers

A marker has the following format.

typedef short MarkerId;

typedef struct {

MarkerId id;

unsigned long position;

pstring markerName;

id is a number that uniquely identifies the marker within a FORM AIFF. The id can be any positive non-zero integer, as long as no other marker within the same FORM AIFF has the same id.

The marker's position in the sound data is determined by position . Markers conceptually fall between two sample frames. A marker that falls before the first sample frame in the sound data is at position zero, while a marker that falls between the first and second sample frame in the sound data is at position 1. Note that the units for position are sample frames, not bytes nor sample points.

markerName is a Pascal-style text string containing the name of the mark.

Note: Some "EA IFF 85" files store strings as C-strings (text bytes followed by a null terminating character) instead of Pascal-style strings. Audio IFF uses pstrings because they are more efficiently skipped over when scanning through chunks. Using pstrings, a program can skip over a string by adding the string count to the address of the first character. C strings require that each character in the string be examined for the null terminator.

Marker Chunk Format

The format for the data within a Marker Chunk is shown below.

#define MarkerID 'MARK' /* ckID for Marker Chunk */

typedef struct {

ID ckID;

long ckSize;

unsigned short numMarkers;

Marker Markers[];

ckID is always 'MARK'. ckSize is the size of the data portion of the chunk, in bytes. It does not include the 8 bytes used by ckID and ckSize.

numMarkers is the number of markers in the Marker Chunk.

numMarkers, if non-zero, it is followed by the markers themselves. Because all fields in a marker are an even number of bytes in length, the length of any marker will always be even. Thus, markers are packed together with no unused bytes between them. The markers need not be ordered in any particular manner.

The Marker Chunk is optional. No more than one Marker Chunk can appear in a FORM AIFF.

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