view vamp-sdk/doc-overview @ 225:f8b38a017d9a distinct-libraries

* branch for clearer distinction between host & plugin libraries

/** \mainpage Vamp Plugin SDK

\section about About Vamp

Vamp is an API for C and C++ plugins that process sampled audio data
to produce descriptive output (measurements or semantic observations).
Find more information at http://www.vamp-plugins.org/ .

Although the official API for Vamp plugins is defined in C for maximum
binary compatibility, we strongly recommend using the provided C++
classes in the SDK to implement your own plugins and hosts.

\section plugins For Plugins

Plugins should subclass Vamp::Plugin, and then use a
Vamp::PluginAdapter to expose the correct C API for the plugin.  Read
the documentation for Vamp::PluginBase and Vamp::Plugin before
starting.

Plugins should be compiled and linked into dynamic libraries using the
usual convention for your platform, and should link (preferably
statically) with -lvamp-sdk.  Any number of plugins can reside in a
single dynamic library.  See plugins.cpp in the example plugins
directory for the sort of code that will need to accompany your plugin
class or classes, to make it possible for a host to look up your
plugins properly.

You will also need to ensure that the entry point
vampGetPluginDescriptor is properly exported (made public) from your
shared library.  The method to do this depends on your linker; for
example, when using the Windows Visual Studio linker, use the linker
flag "/EXPORT:vampGetPluginDescriptor".  Exported symbols are the
default with most other current platforms' linkers.

The following example plugins are provided.  You may legally reuse any
amount of the code from these examples in any plugins you write,
whether proprietary or open-source.

 - 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.

 - 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 bpm 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.

\section hosts For Hosts

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

Starting with version 1.1 of the Vamp SDK, there are several classes
in the Vamp::HostExt namespace that aim to make the host's life as
easy as possible:

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

 - Vamp::HostExt::PluginInputDomainAdapter provides a simple means for
 hosts to handle plugins that expect 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 (new in version 1.2) 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 (new in version 2.0)
 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.

Hosts should link with -lvamp-hostsdk.

(The following notes in this section are mostly relevant for
developers that are not using the HostExt classes, or that wish to
know more about the policy they implement.)

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

\code
vamp:pluginlibrary:pluginname::General Category > Specific Category
\endcode

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.

There is an example host in the "host" directory from which code may
be drawn.

\section license License

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.


*/