An overview of the SMAF file format is shown in the diagram below.
SMAF overview
Under the SMAF specification, constraints are not imposed on the number of tracks, the ordering of tracks and the like. These parameters are instead determined by the practicalities of each individual SMAF application.
Sequence data
Sequence data is defined in terms of "events" and "duration".
The term "event" signifies the use of data to control an output device, as determined by sequence data. The term "duration" signifies the time between events. The time taken to process an event is not "0" in practice; however, for the purposes of SMAF data representation it is regarded as "0", and the passage of time is expressed purely in terms of duration. The time at which a given event occurs can be established by adding the time of the event's first sequence data point to the event's duration. The time taken to process an event does not in principle affect the time at which processing of the next event will start. Thus, successive events which have a duration of "0" are regarded as occurring simultaneously.
Although event processing time is normally regarded as "0", in some cases an event itself includes an internal sub-sequence. An example of this is the GateTime processing performed during a Note event. At the instant at which the Note event occurs, Note ON processing is performed; then, as soon as GateTime has expired, Note OFF processing is carried out. In this instance, GateTime simply expresses the internal expiration time of the Note event, and the execution of subsequent events is not affected. Although some events include more complex sub-sequences, this principle still holds true.
Since SMAF was expressly designed for playback of content, the playback speed can be changed, but the tempo cannot. Since content is played back in real time, tempo and the like are determined by the time resolution.
In addition, when the length of the sequence data which will be used as the units of time is defined, a balance is struck between the degree of precision of data representation and the amount of data involved.
