static void my_audio_callback(const void **start, size_t *size);
*start should be set to point to the region of
memory where your PCM data is stored (16-bit signed integers), and
*size should be the size of this region.
Once you've written your callback, call
rb->pcm_play_data(), and enjoy the music!
rb->pcm_play_data(my_audio_callback, NULL, NULL, 0);