+/** \brief Transition abstract service class
+ *
+ * A transition may modify the output of a producer based on the output of a second producer.
+ *
+ * \extends mlt_service_s
+ * \properties \em a_track the track index (0-based) of a multitrack of the first producer
+ * \properties \em b_track the track index (0-based) of a multitrack of the second producer
+ * \properties \em accepts_blanks a flag to indicate if the transition should accept blank frames
+ * \properties \em always_active a flag to indicate that the in and out points do not apply
+ * \properties \em _transition_type 1 for video, 2 for audio
+ */