Auxiliary audio devices are audio sources, such as CD_ROM audio, mixed with the audio from waveform and internal MIDI synthesizers in a multimedia computer. A software-controlled audio mixer allows applications to control various aspects of the audio mix, such as the relative volume level of each audio source. An auxiliary audio device driver provides the interface between this audio mixer and MMSYSTEM.
To write an auxiliary audio device driver, first create the initialization part of the driver—the part that includes the LibEntry, WEP, and DriverProc entry-point functions. Next, create the auxMessage entry-point function and the support code required to implement the driver. Be sure to process all of the required messages for auxiliary audio device drivers. For each message you process, use the information provided by the reference at the end of this chapter to ensure you did everything required to correctly process the message.