annotate README @ 287:f3b1ba71a305

* When calculating timestamps in order to write them into features that
  previously lacked them, from a buffering adapter, we need to take into
  account any timestamp adjustment used by other wrappers that are being
  wrapped by this one (i.e. input domain adapter)

Vamp
====

An API for audio analysis and feature extraction plugins.

   http://www.vamp-plugins.org/

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

This is version 2.0 of the Vamp plugin Software Development Kit.

Plugins and hosts built with this SDK are binary compatible with those
built using version 1.0 of the SDK, with certain restrictions.  See
the file README.compat for more details.

See the file CHANGELOG for a list of the changes in this release.

A documentation guide to writing plugins using the Vamp SDK can be
found at http://www.vamp-plugins.org/guide.pdf .


Compiling and Installing the SDK and Examples
=============================================

This SDK is intended for use on Windows, OS/X, Linux, and other POSIX
and GNU platforms.

Please see the platform-specific README file (README.msvc, README.osx,
README.linux) in the build/ directory for details about how to compile
and install the SDK, how to build plugin libraries using it, and how
to install the example plugins so you can use them in a host.


What's In This SDK
==================

This SDK 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 the C API is the official API for Vamp, we don't recommend
that you program directly to it.  The C++ abstractions found in the
vamp-sdk and vamp-hostsdk directories (below) are preferable for most
purposes and are more thoroughly documented.


vamp-sdk
--------

C++ classes for implementing Vamp plugins.

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

See "examples" below for details of the example plugins in the SDK,
from which you are welcome to take code and inspiration.

Plugins should link with -lvamp-sdk.


vamp-hostsdk
------------

C++ classes for implementing Vamp hosts.

Hosts will normally use a Vamp::PluginHostAdapter to convert each
plugin's exposed C API back into a useful Vamp::Plugin C++ object.

The Vamp::HostExt namespace contains several additional C++ classes to
do this work for them, and make the host's life easier:

 - Vamp::HostExt::PluginLoader provides a very easy interface for a
 host to discover, load, and find out category information about the
 available plugins.  Most Vamp hosts will probably want to use this
 class.

 - Vamp::HostExt::PluginInputDomainAdapter provides a simple means for
 hosts to handle plugins that want frequency-domain input, without
 having to convert the input themselves.

 - Vamp::HostExt::PluginChannelAdapter provides a simple means for
 hosts to use plugins that do not necessarily support the same number
 of audio channels as they have available, without having to apply a
 channel management / mixdown policy themselves.

 - Vamp::HostExt::PluginBufferingAdapter provides a means for hosts to
 avoid having to negotiate the input step and block size, instead
 permitting the host to use any block size they desire (and a step
 size equal to it).  This is particularly useful for "streaming" hosts
 that cannot seek backwards in the input audio stream and so would
 otherwise need to implement an additional buffer to support step
 sizes smaller than the block size.

 - Vamp::HostExt::PluginSummarisingAdapter provides summarisation
 methods such as mean and median averages of output features, for use
 in any context where an available plugin produces individual values
 but the result that is actually needed is some sort of aggregate.

The PluginLoader class can also use the input domain, channel, and
buffering adapters automatically to make these conversions transparent
to the host if required.

Host authors should also refer to the example host code in the host
directory of the SDK.

Hosts should link with -lvamp-hostsdk.


examples
--------

Example plugins implemented using the C++ classes.

These plugins are intended to be useful examples you can draw code
from in order to provide the basic shape and structure of a Vamp
plugin.  They are also intended to be correct and useful, if simple.

 - 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.

 - PowerSpectrum calculates a power spectrum from the input audio.
 Actually, it doesn't do any work except calculating power from a
 cartesian complex FFT output.  The work of calculating this frequency
 domain output is done for it by the host or host SDK; the plugin just
 needs to declare that it wants frequency domain input.  This is the
 simplest of the example plugins.

 - AmplitudeFollower is a simple implementation of SuperCollider's
 amplitude-follower algorithm.

 - 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.

 - FixedTempoEstimator calculates a single beats-per-minute value
 which is an estimate of the tempo of a piece of music that is assumed
 to be of fixed tempo, using autocorrelation of a frequency domain
 energy rise metric.  It has several outputs that return intermediate
 results used in the calculation, and may be a useful example of a
 plugin having several outputs with varying feature structures.


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.

This host also contains a number of options for listing the installed
plugins and their properties in various formats.  For that reason, it
isn't really as simple as one might hope.  The core of the code is
still reasonably straightforward, however.


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, and a
class (Vamp::HostExt::PluginLoader) that implements a sensible
cross-platform lookup policy using this path.  We recommend using this
class in your host unless you have a good reason not to want to.  This
implementation also permits the user to set the environment variable
VAMP_PATH to override the default path if desired.

The policy used by Vamp::HostExt::PluginLoader -- and our
recommendation for any host -- is to search each directory in the path
returned by getPluginPath 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.  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 plugin's API itself.  The Vamp::HostExt::PluginLoader class also
provides support for plugin category lookup using this scheme.


Licensing
=========

This plugin SDK is freely redistributable under a "new-style BSD"
licence.  See the file COPYING for more details.  In short, you may
modify and redistribute the SDK and example plugins within any
commercial or non-commercial, proprietary or open-source plugin or
application under almost any conditions, with no obligation to provide
source code, 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/


Authors
=======

Vamp and the Vamp SDK were designed and made at the Centre for Digital
Music at Queen Mary, University of London.

The SDK was written by Chris Cannam, copyright (c) 2005-2008
Chris Cannam and QMUL.

Mark Sandler and Christian Landone provided ideas and direction, and
Mark Levy, Dan Stowell, Martin Gasser and Craig Sapp provided testing
and other input for the 1.0 API and SDK.  The API also uses some ideas
from prior plugin systems, notably DSSI (http://dssi.sourceforge.net)
and FEAPI (http://feapi.sourceforge.net).