When calling Mix_OpenAudio, can either pick your own values, or use some
#define'd defaults:
int freq, channels;
Uint16 format;
/* Open audio: */
Mix_OpenAudio(MIX_DEFAULT_FREQUENCY,
MIX_DEFAULT_FORMAT,
MIX_DEFAULT_CHANNELS, 512);
/* Find out what was actually set: */
Mix_QuerySpec(&frequency, &format, &channels);