annotate README @ 40:ae3e47e76d2d

* Add plugin path traversal and plugin listing option to vamp-simple-host
* Add more notes on plugin lookup and categorisation

Vamp
====
http://www.sonicvisualiser.org/vamp.html

An API for audio analysis and feature extraction plugins.

Vamp is an API for C and C++ plugins that process sampled audio data
to produce descriptive output (measurements or semantic observations).

The principal differences between Vamp and a real-time audio
processing plugin system such as VST are:

 * Vamp plugins may output complex multidimensional data with labels.
   As a consequence, they are likely to work best when the output
   data has a much lower sampling rate than the input.  (This also
   means it is usually desirable to implement them in C++ using the
   high-level base class provided rather than use the raw C API.)

 * While Vamp plugins receive data block-by-block, they are not
   required to return output immediately on receiving the input.
   A Vamp plugin may be non-causal, preferring to store up data
   based on its input until the end of a processing run and then
   return all results at once.

 * Vamp plugins have more control over their inputs than a typical
   real-time processing plugin.  For example, they can indicate to
   the host their preferred processing block and step sizes, and these
   may differ.

 * Vamp plugins may ask to receive data in the frequency domain
   instead of the time domain.  The host takes the responsibility
   for converting the input data using an FFT of windowed frames.
   This simplifies plugins that do straightforward frequency-domain
   processing and permits the host to cache frequency-domain data
   when possible.

 * A Vamp plugin is configured once before each processing run, and
   receives no further parameter changes during use -- unlike real
   time plugin APIs in which the input parameters may change at any
   time.  This also means that fundamental properties such as the
   number of values per output or the preferred processing block
   size may depend on the input parameters.

 * Vamp plugins do not have to be able to run in real time.

Vamp reuses some ideas from several existing systems, notably DSSI
(http://dssi.sourceforge.net) and FEAPI (http://feapi.sourceforge.net).


About this SDK
==============

This Software Development Kit contains the following:

 * vamp/vamp.h

The formal C language plugin API for Vamp plugins.

A Vamp plugin is a dynamic library (.so, .dll or .dylib depending on
platform) exposing one C-linkage entry point (vampGetPluginDescriptor)
which returns data defined in the rest of this C header.

Although this is the official API for Vamp, we don't recommend that
you program directly to it.  The C++ abstraction in the SDK directory
(below) is likely to be preferable for most purposes, and is better
documented.

 * vamp-sdk

C++ classes for straightforwardly implementing Vamp plugins and hosts.

Plugins should subclass Vamp::Plugin and then use a
Vamp::PluginAdapter to expose the correct C API for the plugin.  Read
vamp-sdk/PluginBase.h and Plugin.h for code documentation.

Hosts may use the Vamp::PluginHostAdapter to convert the loaded
plugin's C API back into a Vamp::Plugin object.

 * examples

Example plugins implemented using the C++ classes.  ZeroCrossing
calculates the positions and density of zero-crossing points in an
audio waveform.  SpectralCentroid calculates the centre of gravity of
the frequency domain representation of each block of audio.
PercussionOnsetDetector estimates the locations of percussive onsets
using a simple method described in "Drum Source Separation using
Percussive Feature Detection and Spectral Modulation" by Dan Barry,
Derry Fitzgerald, Eugene Coyle and Bob Lawlor, ISSC 2005.

 * host

A simple command-line Vamp host, capable of loading a plugin and using
it to process a complete audio file, with its default parameters.
Requires libsndfile.


Plugin Lookup and Categorisation
================================

The Vamp API does not officially specify how to load plugin libraries
or where to find them.  However, the SDK does include a function
(Vamp::PluginHostAdapter::getPluginPath()) that returns a recommended
directory search path that hosts may use for plugin libraries.

Our suggestion for a host is to search each directory in this path for
.DLL (on Windows), .so (on Linux, Solaris, BSD etc) or .dylib (on
OS/X) files, then to load each one and perform a dynamic name lookup
on the vampGetPluginDescriptor function to enumerate the plugins in
the library.  The example host has some code that may help, but this
operation will necessarily be system-dependent.

Vamp also has an informal convention for sorting plugins into
functional categories.  In addition to the library file itself, a
plugin library may install a category file with the same name as the
library but .cat extension.  The existence and format of this file are
not specified by the Vamp API, but by convention the file may contain
lines of the format

vamp:pluginlibrary:pluginname::General Category > Specific Category

which a host may read and use to assign plugins a location within a
category tree for display to the user.  The expectation is that
advanced users may also choose to set up their own preferred category
trees, which is why this information is not queried as part of the
Vamp API itself.


Building the SDK
================

Edit the Makefile to suit your platform according to the comments in
it.  Type "make".


Licensing
=========

This plugin SDK is freely redistributable under a "new-style BSD"
licence.  See the file COPYING for more details.  In short, you are
permitted to reuse the SDK and example plugins in any commercial or
non-commercial, proprietary or open-source application or plugin under
almost any conditions provided you retain the original copyright note.


See Also
========

Sonic Visualiser, an interactive open-source graphical audio
inspection, analysis and visualisation tool supporting Vamp plugins.
http://www.sonicvisualiser.org/


Chris Cannam
Centre for Digital Music
Queen Mary, University of London