clap

Audio Plugin API

free-audio
1810
103
C

CLAP

Learn about CLAP

CLAP stands for CLever Audio Plugin. It is an interface that
provides a stable ABI to define a standard for Digital Audio Workstations and
audio plugins (synthesizers, audio effects, …) to work together.

The ABI, or Application Binary Interface, serves as a means of
communication between a host and a plugin. It provides backwards compatibility,
that is, a plugin binary compiled with CLAP 1.x can be loaded by any other
CLAP 1.y.

To work with CLAP, include clap/clap.h.
To also include the draft extensions, include clap/all.h.

The two most important objects are clap_host and clap_plugin.

src/plugin-template.c is a very minimal example which demonstrates how to wire a CLAP plugin.

Entry point

The entry point is declared in entry.h.

Extensions

Most features come from extensions, which are in fact C interfaces.

// host extension
const clap_host_log *log = host->extension(host, CLAP_EXT_LOG);
if (log)
   log->log(host, CLAP_LOG_INFO, "Hello World! ;^)");

// plugin extension
const clap_plugin_params *params = plugin->extension(plugin, CLAP_EXT_PARAMS);
if (params)
{
   uint32_t paramsCount = params->count(plugin);
   // ...
}

The extensions are defined in the ext folder.

Some extensions are still in the progress of being designed and they are in
the draft folder.

An extension comes with:

  • a header #include <clap/ext/xxx.h>
  • an extension identifier: #define CLAP_EXT_XXX "clap/XXX"
  • host interfaces are named like: struct clap_host_xxx
  • plugin interfaces are named like: struct clap_plugin_xxx
  • each method must have a clear thread specification

You can create your own extensions and share them. Make sure that the extension identifier:

  • includes versioning in case the ABI breaks
  • is a unique identifier

All strings are valid UTF-8.

Fundamental extensions

This is a list of the extensions that you most likely want to implement
and use to get a basic plugin experience:

  • state, save and load the plugin state
    • state-context, same as state but with additional context info (preset, duplicate, project)
    • resource-directory, host provided folder for the plugin to save extra resource like multi-samples, … (draft)
  • params, parameters management
  • note-ports, define the note ports
  • audio-ports, define the audio ports
  • render, renders realtime or offline
  • latency, report the plugin latency
  • tail, processing tail length
  • gui, generic gui controller
  • voice-info, let the host know how many voices the plugin has, this is important for polyphonic modulations
  • track-info, give some info to the plugin about the track it belongs to
  • tuning, host provided microtuning (draft)
  • triggers, plugin’s triggers, similar to parameters but stateless

Support extensions

  • thread-check, check which thread you are currently on, useful for correctness validation
  • thread-pool, use the host thread pool
  • log, lets the host aggregate plugin logs
  • timer-support, lets the plugin register timer handlers
  • posix-fd-support, lets the plugin register I/O handlers

Deeper Host integration

  • remote-controls, bank of controls that can be mapped on a controlles with 8 knobs
  • preset-discovery, let the host index the plugin’s preset in their native file format
  • preset-load, let the host ask the plugin to load a preset
  • param-indication, let the plugin know when a physical control is mapped to a parameter and if there is automation data
  • note-name, give a name to notes, useful for drum machines
  • transport-control, let the plugin control the host’s transport (draft)
  • context-menu, exchange context menu entries between host and plugin, let the plugin ask the host to popup its own context menu

Third-party extensions

Adapters

  • clap-wrapper, wrappers for using CLAP in other plugin environments

Resources

  • clap-validator, a validator and automatic test suite for CLAP plugins.
  • clapdb, a list of plugins and DAWs which supports CLAP

Examples

Community related projects

  • clap-juce-extension, juce add-on
  • MIP2, host and plugins
  • Avendish, a reflection-based API for media plug-ins in C++ which supports Clap
  • NIH-plug, an API-agnostic, Rust-based plugin framework aiming to reduce boilerplate without getting in your way
  • iPlug2, a liberally licensed C++ audio plug-in framework that supports Clap

Programming Language Bindings

Artwork