Opening
and Closing Mixer Devices
When you want
to use a mixer device, you can either simply begin using it or you can
explicitly open the device before using it. Explicitly opening a mixer device
offers two main benefits:
It guarantees the continued
existence of that mixer device.
It lets you receive
notification of audio line and control changes.
You can use
the mixerOpen function
to explicitly open a mixer device. This function takes as parameters a device
identifier, a pointer to a memory location, and other values unique to each
type of device. The memory location is filled with a device handle. Use this
device handle to identify the open mixer device when calling other audio mixer
functions. As long as a handle of a mixer device exists, the device continues
to exist in the system. If a configuration change occurs to the mixer device
and it hasn t been explicitly opened, your application might suddenly be unable
to access it.
Note The difference
between device identifiers and device handles is important. Device handles are
returned when you open a device driver by using mixerOpen. Device
identifiers are determined implicitly from the number of devices present in a
system; this number is obtained by using the mixerGetNumDevs function.
You can use
the mixerClose function
to close a mixer device. You should close the device after you finish using it.