- * This parameter may be NULL, which signals the end of the stream (i.e. no more
- * packets will be sent). That will cause the filter to output any packets it
- * may have buffered internally.
+ * If pkt is empty (i.e. NULL, or pkt->data is NULL and pkt->side_data_elems zero),
+ * it signals the end of the stream (i.e. no more non-empty packets will be sent;
+ * sending more empty packets does nothing) and will cause the filter to output
+ * any packets it may have buffered internally.