text: snd_mixer_read()
  Read pending mixer events
  Synopsis:
  #include <sys/asoundlib.h> int snd_mixer_read( snd_mixer_t *handle, snd_mixer_callbacks_t *callbacks );
  Arguments:
  - handle
  - The handle for the mixer device. This must have been created by snd_mixer_open() .
  - callbacks
  - A pointer to a snd_mixer_callbacks_t structure that defines the list of callbacks.
  Library:
  libasound.so
  Use the -l asound option to qcc to link against this library.
  Description:
  The snd_mixer_read() function reads pending mixer events from the mixer handle. As each event is read, the list of callbacks is checked for a handler for this event. If a match is found, the callback is invoked. This function is usually called when the select() library call indicates that there is data to be read on the mixer's file descriptor.