-/** Try to get `frames' frames of audio and copy it into `out'. Silence
- * will be filled if no audio is available.
- * @return time of this audio, or unset if there was a buffer underrun.
+/** Try to get `frames' frames of audio and copy it into `out'.
+ * @param behaviour BLOCKING if we should block until audio is available. If behaviour is NON_BLOCKING
+ * and no audio is immediately available the buffer will be filled with silence and boost::none
+ * will be returned.
+ * @return time of this audio, or unset if blocking was false and no data was available.