+/** \brief Producer abstract service class
+ *
+ * A producer is a service that generates audio, video, and metadata.
+ * Some day it may also generate text (subtitles). This is not to say
+ * a producer "synthesizes," rather that is an origin of data within the
+ * service network - that could be through synthesis or reading a stream.
+ *
+ * \extends mlt_service
+ * \event \em producer-changed
+ * \properties \em mlt_type the name of the service subclass, e.g. mlt_producer
+ * \properties \em mlt_service the name of a producer subclass
+ * \properties \em _position the current position of the play head, relative to the in point
+ * \properties \em _frame the current position of the play head, relative to the beginning of the resource
+ * \properties \em _speed the current speed factor, where 1.0 is normal
+ * \properties \em aspect_ratio sample aspect ratio
+ * \properties \em length the duration of the cut in frames
+ * \properties \em eof the end-of-file behavior, one of: pause, continue, loop
+ * \properties \em resource the file name, stream address, or the class name in angle brackets
+ * \properties \em _cut set if this producer is a "cut" producer
+ * \properties \em mlt_mix stores the data for a "mix" producer
+ * \properties \em _cut_parent holds a reference to the cut's parent producer
+ * \properties \em ignore_points Set this to temporarily disable the in and out points.
+ * \properties \em use_clone holds a reference to a clone's producer, as created by mlt_producer_optimise
+ * \properties \em _clone is the index of the clone in the list of clones stored on the clone's producer
+ * \properties \em _clones is the number of clones of the producer, as created by mlt_producer_optimise
+ * \properties \em _clone.{N} holds a reference to the N'th clone of the producer, as created by mlt_producer_optimise
+ * \properties \em meta.* holds metadata - there is a loose taxonomy to be defined
+ * \properties \em set.* holds properties to set on a frame produced
+ * \todo define the media metadata taxonomy
+ */