QuickTime Music Architecture

Marker Event

The marker event has three subtypes. The end marker event ( Figure 8 ) marks the end of a series of events. The beat marker event marks the beat and the tempo marker event indicates the tempo.

Figure 8 Marker event of subtype end

Table 5 Contents of a marker event
Marker event type	First nibble value = `011X`
Subtype	8-bit unsigned subtype
Value	16-bit signed value

The marker subtype bit field contains zero for an end marker (kMarkerEventEnd ), 1 for a beat marker (kMarkerEventBeat ), or 2 for a tempo marker (kMarkerEventTempo ).

The value bit field varies according to the subtype:

For an end marker event, a value of 0 means stop; any other value is reserved.
For a beat marker event, a value of 0 is a single beat (a quarter note); any other value indicates the number of fractions of a beat in 1/65536 beat.
For a tempo marker event, the value is the same as a beat marker, but indicates that a tempo event should be computed (based on where the next beat or tempo marker is) and emitted upon export.

Use this macro call to stuff the marker event's long word:



 
qtma_StuffMarkerEvent(x, markerType, markerValue)

Use these macro calls to extract fields from the marker events long word:



 
qtma_MarkerSubtype(x)

qtma_MarkerValue(x)