1. Introduction

LADSPA is the Linux Audio Developers' Simple Plugin Architecture.

This document describes how to write LADSPA plugins and how to write hosts, which are programs that use LADSPA plugins,

This documentation is currently extremely incomplete.

Please be aware that the ladspa.h file is the official, definitive guide to the standard.

1.1 Terminology

There are several common bits of terminology:

plugin library

A shared library that can be loaded and unloaded "on-the-fly". Under linux we open plugins using the dlopen function.

plugin

a single sound-producing/consuming type identified with a descriptor whose C-type is LADSPA_Descriptor. A plugin library may contain several plugin descriptors, each with an index within plugin library. The indices must be consecutive and start with 0.

plugin instance

is a single running unit generator. There is a standard way to make plugin instances from plugins. In the host, we identify the instance by a handle whose type is void*.

host

The program which will load the plugins.

The standard describes the binary interface for a plugin library to present its plugins to the host.

1.2 The Plugin Lifecycle

• the plugin library is loaded (using a system-specific method like dlopen or for glib, gtk+ users, g_module_open).
• the plugin descriptor is obtained using the plugin library's ladspa_descriptor function, which may allocate memory.
• the host uses the plugin's instantiate function to allocate a new (or several new) sample-processing instances.
• the host must connect buffers to every one of the plugin's ports. It must also call activate before running samples through the plugin.
• the host processes sample data with the plugin by filling the input buffers it connected, then calling either run or run_adding. The host may reconnect ports with connect_port as it sees fit.
• the host deactivates the plugin handle. It may opt to activate and reuse the handle, or it may destroy the handle.
• the handle is destroyed using the cleanup function.
• the plugin is closed. Its _fini function is responsible for deallocating memory.