annotate src/doc-overview @ 277:6d355f1b7eaf

* Patch from Richard Ash to make building the host optional, so you can
  at least build the SDK even if you don't have libsndfile

/** \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.

Please read the relevant README file for your platform found in the
Vamp SDK build/ directory, for details about how to ensure the
resulting dynamic library exports the correct linker symbols.

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.

 - 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.

\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.

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.

(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, 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 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 plugin's API itself.  The Vamp::HostExt::PluginLoader class also
provides support for plugin category lookup using this scheme.

\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.


*/