If our window isn't the foreground window, we'll never be able to
successfully Acquire with SetCooperativeLevel DISCL_FOREGROUND in effect.

The ICNS support is only used on Mac OS X and is not anticipated to be used
on any other platform.  So, we can rely on the native frameworks rather than
a third-party dependency.

ICNS files can store multiple sizes, like ICOs.

There are three different units to represent durations of audio: time,
bytes, and frames. Since all three are in use in this module, we should
be more explicit about the unit of each variable.