- /* Called when the mute setting is queried. Called from main loop
- * context. If this is NULL a PA_SOURCE_MESSAGE_GET_MUTE message
- * will be sent to the IO thread instead. If refresh_mute is
- * false neither this function is called nor a message is sent.
+ /* If the source mute can change "spontaneously" (i.e. initiated by the
+ * source implementation, not by someone else calling
+ * pa_source_set_mute()), then the source implementation can notify about
+ * changed mute either by calling pa_source_mute_changed() or by calling
+ * pa_source_get_mute() with force_refresh=true. If the implementation
+ * chooses the latter approach, it should implement the get_mute callback.
+ * Otherwise get_mute can be NULL.
+ *
+ * This is called when pa_source_get_mute() is called with
+ * force_refresh=true. This is called from the IO thread if the
+ * PA_SINK_DEFERRED_VOLUME flag is set, otherwise this is called from the
+ * main thread. On success, the implementation is expected to return 0 and
+ * set the mute parameter that is passed as a reference. On failure, the
+ * implementation is expected to return -1.