This extension defines the format for "messages" which can be used to dynamically control an LV2 plugin instance at runtime. Messages are useful for any kind of plugin control that does not fit well with control ports. Plugins can both receive and send messages (and thus send messages to each other) via any mechanism. This extension requires the host to support the LV2 URI Map extension, and the LV2 Atom extension.
Base class for all types of LV2 Message. A type of message, which must be a resource (i.e. have a URI). This URI is used as the selector component of a Message and is used by receivers to interpret the meaning of messages (e.g. which components are present).
A message is a communication from one component to another. Messages consist of a selector URI, and a key/value dictionary. Keys in the dictionary are URI mapped integers, and values are Atoms. The selector URI dictates how the message is to be interpreted (e.g. the selector can be used as a "verb" to build commands). Messages are simple to serialise in many different formats (e.g. any RDF serialisation including LV2 Turtle files, JSON, XML, etc) making network transparency and persistence simple, assuming the implementation can serialise Atoms. Because all messages have a standard format, plugins and hosts can store, communicate, or otherwise work with messages even if they do not understand that particular message's selector. In memory, a Message is simply a uint32_t selector (a URI mapped integer) followed by an atom:Blank.