aRts is not only a piece of software, it also provides a variety of APIs for a variety of purposes. In this section, I will try to describe the "big picture", a brief glance what those APIs are supposed to do, and how they interact.
There is one important distinction to make: most of the APIs are language and location independant because they are specified as mcopidl. That is, you can basically use the services they offer from any language, implement them in any language, and you will not have to care whether you are talking to local or remote objects. Here is a list of these first:
Basic definitions that form the core of the MCOP functionality, such as the protocol itself, definitions of the object, the trader, the flow system and so on.
These contain the flow system you will use for connecting audio streams, the definition of Arts::SynthModule which is the base for any interface that has streams, and finally a few useful audio objects
Here, an object that can play a media, Arts::PlayObject gets defined. Media players such as the KDE media player noatun will be able to play any media for which a PlayObject can be found. So it makes sense to implement PlayObjects for various formats (such as mp3, mpg video, midi, wav, ...) on that base, and there are a lot already.
Here, an interface for the system wide sound server artsd is defined. The interface is called Arts::SoundServer, which implements functionality like accepting streams from the network, playing samples, creating custom other aRts objects and so on. Network transparency is implied due to the use of MCOP (as for everything else here).
This module defines basic flow graph functionality, that is, combining simpler objects to more complex ones, by defining a graph of them. It defines the basic interface Arts::StructureDesc, Arts::ModuleDesc and Arts::PortDesc which contain a description of a structure, module, and port. There is also a way to get a "living network of objects" out of these connection and value descriptions, using a factory.
This module defines basic midi functionality, like objects that produce midi events, what is a midi event, an Arts::MidiManager to connect the producers and consumers of midi events, and so on. As always network transparency implied.
Here are various additional filters, oscillators, effects, delays and so on, everything required for real useful signal processing, and to build complex instruments and effects out of these basic building blocks.
This cares about visual objects. It defines the basic type Arts::Widget from which all GUI modules derive. This will produce toolkit independency, and ... visual GUI editing, and serializable GUIs. Also, as the GUI elements have normal attributes, their values can be straight forward connected to some signal processing modules. (I.e. the value of a slider to the cutoff of a filter). As always: network transparent.
Where possible, aRts itself is implemented using IDL. On the other hand, there are some language specific APIs, using either plain C++ or plain C. It is usually wise to use IDL interfaces where possible, and the other APIs where necessary. Here is a list of language specific APIs:
These are convenience KDE APIs for the simple and common common case, where you just want to play a sample. The APIs are plain C++, Qt/KDE optimized, and as easy as it can get.
Plain C interface for the sound server. Very useful for porting legacy applications.
Here all magic for MCOP happens. The library contains the basic things you need to know for writing a simple MCOP application, the dispatcher, timers, iomanagement, but also the internals to make the MCOP protocol itself work.
Besides the implementation of artsflow.idl, some useful utilities like sampling rate conversion.
Integration of MCOP into the Qt event loop, when you write Qt applications using MCOP.