QuickTime Music Architecture

Note Allocator Component

You use the note allocator component to play individual notes. Your application can specify which musical instrument sound to use and exactly which music synthesizer to play the notes on. The note allocator component can also display an Instrument Picker, which allows the user to choose instruments. The note allocator, unlike the tune player, provides no timing-related features to manage a sequence of notes. Its features are similar to a music component, although more generalized. Typically, an application opens a connection to the note allocator, which in turn sends messages to the music component. An application or movie music track can incorporate any number of musical timbres or parts.

To play a single note, your application must open a connection to the note allocator component and call NANewNoteChannel with a note request--typically to request a standard instrument within the General MIDI library of instruments. A note channel is similar in some ways to a Sound Manager sound channel in that it needs to be created and disposed of, and can receive various commands. The note allocator provides an application-level interface for requesting note channels with particular attributes. The client specifies the desired polyphony and the desired tone. The note allocator returns a note channel that best satisfies the request.

With an open note channel, an application can call NAPlayNote while specifying the note's pitch and velocity. The note is played and continues to play until a second call to NAPlayNote is made specifying the same pitch but with a velocity of zero. The velocity of zero causes the note to stop. The note allocator functions let you play individual notes, apply a controller change, apply a knob change, select an instrument based on a required tone, and modify or change the instrument type on an existing note channel.

There are calls for registering and unregistering a music component. As part of registration, the MIDI connections, if applicable, are specified. There is also a call for querying the note allocator for registered music components, so that an application can offer a selection of the existing devices to the user.