When the event occurs and the operating system calls the callback routine, this routine calls midiOutShortMsg to turn on or turn off one or more scheduled notes. ![]() This call takes as one of its parameters a function pointer to the application's callback routine. The main loop of a typical MIDI-playback application calls timeSetEvent to schedule the next note-on or note-off event. All of the other components in the figure are system-supplied. If appropriate, a vendor might choose to use one of the system-supplied miniport drivers-FMSynth, UART, or DMusUART-instead of writing a custom miniport driver. The MIDI and DMus miniport drivers are shown as darkened boxes to indicate that they can be vendor-supplied components. The MIDI application in the preceding figure reads time-stamped MIDI events from a MIDI file and plays them. This application interfaces to the WDM audio drivers through the midiOut Xxx functions, which are implemented in the WinMM system component, Winmm.dll. The following figure shows the user-mode and kernel-mode components that a MIDI application uses to play back MIDI data. Graph building is transparent to the applications that use these software interfaces. ![]() For more information about DirectMusic and the Windows Multimedia MIDI functions, see the Microsoft Windows SDK documentation.ĭirectMusic and the Windows Multimedia MIDI functions are clients of the SysAudio system driver, which builds the audio filter graphs that process the MIDI and DirectMusic streams. However, by emulating the behavior of older software and hardware, the midiOut Xxx and midiIn Xxx functions sacrifice the precision timing and enhanced functionality that are now available through the DirectMusic API. Beginning with Windows 98, the WDMAud system driver translates calls to these functions into commands to WDM audio drivers. The behavior of the midiOut Xxx and midiIn Xxx functions is based on the capabilities of legacy MIDI drivers and devices. ![]() Microsoft Windows Multimedia midiOut Xxx and midiIn Xxx functions ![]() Application programs rely on a combination of user- and kernel-mode components to capture and play back MIDI and DirectMusic streams.Īn application can use either of the following software interfaces for MIDI playback and capture:
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