@prefix lv2: <http://lv2plug.in/ns/lv2core#> .
@prefix doap: <http://usefulinc.com/ns/doap#> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

<http://lv2plug.in/ns/lv2core>
	a doap:Project ;
	doap:license <http://opensource.org/licenses/isc> ;
	doap:name "LV2" ;
	doap:homepage <http://lv2plug.in> ;
	doap:created "2004-04-21" ;
	doap:shortdesc "An extensible open standard for audio plugins" ;
	doap:programming-language "C" ;
	doap:developer <http://plugin.org.uk/swh.xrdf#me> ,
		<http://drobilla.net/drobilla#me> ;
	doap:maintainer <http://drobilla.net/drobilla#me> ;
	lv2:documentation """

LV2 is an interface for writing audio plugins in C or compatible languages,
which can be dynamically loaded into many _host_ applications.  This core
specification is simple and minimal, but is designed so that _extensions_ can
be defined to add more advanced features, making it possible to implement
nearly any feature.

LV2 maintains a strong distinction between code and data.  Plugin code is in a
shared library, while data is in a companion data file written in
[Turtle](https://www.w3.org/TR/turtle/).  Code, data, and any other resources
(such as waveforms) are shipped together in a bundle directory.  The code
contains only the executable portions of the plugin.  All other data is
provided in the data file(s).  This makes plugin data flexible and extensible,
and allows the host to do everything but run the plugin without loading or
executing any code.  Among other advantages, this makes hosts more robust
(broken plugins can't crash a host during discovery) and allows generic tools
written in any language to work with LV2 data.  The LV2 specification itself is
distributed in a similar way.

An LV2 plugin library is suitable for dynamic loading (for example with
`dlopen()`) and provides one or more plugin descriptors via `lv2_descriptor()`
or `lv2_lib_descriptor()`.  These can be instantiated to create plugin
instances, which can be run directly on data or connected together to perform
advanced signal processing tasks.

Plugins communicate via _ports_, which can transmit any type of data.  Data is
processed by first connecting each port to a buffer, then repeatedly calling
the `run()` method to process blocks of data.

This core specification defines two types of port, equivalent to those in
[LADSPA](http://www.ladspa.org/), lv2:ControlPort and lv2:AudioPort, as well as
lv2:CVPort which has the same format as an audio port but is interpreted as
non-audible control data.  Audio ports contain arrays with one `float` element
per sample, allowing a block of audio to be processed in a single call to
`run()`.  Control ports contain single `float` values, which are fixed and
valid for the duration of the call to `run()`.  Thus the _control rate_ is
determined by the block size, which is controlled by the host (and not
necessarily constant).

### Threading Rules

To facilitate use in multi-threaded programs, LV2 functions are partitioned into
several threading classes:

| Discovery Class                  | Instantiation Class           | Audio Class                    |
|----------------------------------|-------------------------------|------------------------------- |
| lv2_descriptor()                 | LV2_Descriptor::instantiate() | LV2_Descriptor::run()          |
| lv2_lib_descriptor()             | LV2_Descriptor::cleanup()     | LV2_Descriptor::connect_port() |
| LV2_Descriptor::extension_data() | LV2_Descriptor::activate()    |                                |
|                                  | LV2_Descriptor::deactivate()  |                                |

Hosts MUST guarantee that:

 * A function in any class is never called concurrently with another function
   in that class.

 * A _Discovery_ function is never called concurrently with any other function
   in the same shared object file.

 * An _Instantiation_ function for an instance is never called concurrently
   with any other function for that instance.

Any simultaneous calls that are not explicitly forbidden by these rules are
allowed. For example, a host may call `run()` for two different plugin
instances simultaneously.

Plugin functions in any class MUST NOT manipulate any state which might affect
other plugins or the host (beyond the contract of that function), for example
by using non-reentrant global functions.

Extensions to this specification which add new functions MUST declare in which
of these classes the functions belong, define new classes for them, or
otherwise precisely describe their threading rules.

"""^^lv2:Markdown .

lv2:Specification
	lv2:documentation """

An LV2 specification typically contains a vocabulary description, C headers to
define an API, and any other resources that may be useful.  Specifications,
like plugins, are distributed and installed as bundles so that hosts may
discover them.

"""^^lv2:Markdown .

lv2:Markdown
	lv2:documentation """

This datatype is typically used for documentation in
[Markdown](https://daringfireball.net/projects/markdown/syntax) syntax.

Generally, documentation with this datatype should stay as close to readable
plain text as possible, but may use core Markdown syntax for nicer
presentation.  Documentation can assume that basic extensions like codehilite
and tables are available.

"""^^lv2:Markdown .

lv2:documentation
	lv2:documentation """

Relates a Resource to extended documentation.

LV2 specifications are documented using this property with an lv2:Markdown
datatype.

If the value has no explicit datatype, it is assumed to be a valid XHTML Basic
1.1 fragment suitable for use as the content of the `body` element of a page.

XHTML Basic is a W3C Recommendation which defines a simplified subset of XHTML
intended to be reasonable to implement with limited resources, for exampe on
embedded devices. See [XHTML Basic, Section
3](http://www.w3.org/TR/xhtml-basic/#s_xhtmlmodules) for a list of valid tags.

"""^^lv2:Markdown .

lv2:PluginBase
	lv2:documentation """

An abstract plugin-like resource that may not actually be an LV2 plugin, for
example that may not have a lv2:binary.  This is useful for describing things
that share common structure with a plugin, but are not themselves an actual
plugin, such as presets.

"""^^lv2:Markdown .

lv2:Plugin
	lv2:documentation """

To be discovered by hosts, plugins MUST explicitly have an rdf:type of lv2:Plugin
in their bundle's manifest, for example:

    :::turtle
    <http://example.org/my-plugin> a lv2:Plugin .

Plugins should have a doap:name property that is at most a few words in length
using title capitalization, for example <q>Tape Delay Unit</q>.

"""^^lv2:Markdown .

lv2:PortBase
	lv2:documentation """

Similar to lv2:PluginBase, this is an abstract port-like resource that may not
be a fully specified LV2 port.  For example, this is used for preset "ports"
which do not specify an index.

"""^^lv2:Markdown .

lv2:Port
	lv2:documentation """

All LV2 port descriptions MUST have a rdf:type that is one of lv2:Port,
lv2:InputPort or lv2:OutputPort.  Additionally, there MUST be at least one
other rdf:type which more precisely describes type of the port, for example
lv2:AudioPort.

Hosts that do not support a specific port class MUST NOT instantiate the
plugin, unless that port has the lv2:connectionOptional property set.

A port has two identifiers: a (numeric) index, and a (textual) symbol.  The
index can be used as an identifier at run-time, but persistent references to
ports (for example in presets or save files) MUST use the symbol.  Only the
symbol is guaranteed to refer to the same port on all plugins with a given URI,
that is the index for a port may differ between plugin binaries.

"""^^lv2:Markdown .

lv2:AudioPort
	lv2:documentation """

Ports of this type are connected to a buffer of `float` audio samples, which
the host guarantees have `sample_count` elements in any call to
LV2_Descriptor::run().

Audio samples are normalized between -1.0 and 1.0, though there is no
requirement for samples to be strictly within this range.

"""^^lv2:Markdown .

lv2:CVPort
	lv2:documentation """

Ports of this type have the same buffer format as an lv2:AudioPort, except the
buffer represents audio-rate control data rather than audio.  Like a
lv2:ControlPort, a CV port SHOULD have properties describing its value, in
particular lv2:minimum, lv2:maximum, and lv2:default.

Hosts may present CV ports to users as controls in the same way as control
ports.  Conceptually, aside from the buffer format, a CV port is the same as a
control port, so hosts can use all the same properties and expectations.

In particular, this port type does not imply any range, unit, or meaning for
its values.  However, if there is no inherent unit to the values, for example
if the port is used to modulate some other value, then plugins SHOULD use a
normalized range, either from -1.0 to 1.0, or from 0.0 to 1.0.

It is generally safe to connect an audio output to a CV input, but not
vice-versa.  Hosts must take care to prevent data from a CVPort port from being
used as audio.

"""^^lv2:Markdown .

lv2:project
	lv2:documentation """

This property provides a way to group plugins and/or related resources.  A
project may have useful metadata common to all plugins (such as homepage,
author, version history) which would be wasteful to list separately for each
plugin.

Grouping via projects also allows users to find plugins in hosts by project,
which is often how they are remembered.  For this reason, a project that
contains plugins SHOULD always have a doap:name.  It is also a good idea for
each plugin and the project itself to have an lv2:symbol property, which allows
nice quasi-global identifiers for plugins, for example `myproj.superamp` which
can be useful for display or fast user entry.

"""^^lv2:Markdown .

lv2:prototype
	lv2:documentation """

This property can be used to <q>include</q> common properties in several
descriptions, serving as a sort of template mechanism.  If a plugin has a
prototype, then the host must load all the properties for the prototype as if
they were properties of the plugin.  That is, if `:plug lv2:prototype :prot`,
then for each triple `:prot p o`, the triple `:plug p o` should be loaded.

This facility is useful for distributing data-only plugins that rely on a
common binary, for example those where the internal state is loaded from some
other file.  Such plugins can refer to a prototype in a template LV2 bundle
which is installed by the corresponding software.

"""^^lv2:Markdown .

lv2:minorVersion
	lv2:documentation """

This, along with lv2:microVersion, is used to distinguish between different
versions of the <q>same</q> resource, for example to load only the bundle with
the most recent version of a plugin.  An LV2 version has a minor and micro
number with the usual semantics:

  * The minor version MUST be incremented when backwards (but not forwards)
    compatible additions are made, for example the addition of a port to a
    plugin.

  * The micro version is incremented for changes which do not affect
    compatibility at all, for example bug fixes or documentation updates.

Note that there is deliberately no major version: all versions with the same
URI are compatible by definition.  Replacing a resource with a newer version of
that resource MUST NOT break anything.  If a change violates this rule, then
the URI of the resource (which serves as the major version) MUST be changed.

Plugins and extensions MUST adhere to at least the following rules:

  * All versions of a plugin with a given URI MUST have the <q>same</q> set of
    mandatory (not lv2:connectionOptional) ports with respect to lv2:symbol and
    rdf:type.  In other words, every port on a particular version is guaranteed
    to exist on a future version with same lv2:symbol and at least those
    rdf:types.

  * New ports MAY be added without changing the plugin URI if and only if they
    are lv2:connectionOptional and the minor version is incremented.

  * The minor version MUST be incremented if the index of any port (identified
    by its symbol) is changed.

  * All versions of a specification MUST be compatible in the sense that an
    implementation of the new version can interoperate with an implementation
    of any previous version.

Anything that depends on a specific version of a plugin (including referencing
ports by index) MUST refer to the plugin by both URI and version.  However,
implementations should be tolerant where possible.

When hosts discover several installed versions of a resource, they SHOULD warn
the user and load only the most recent version.

An odd minor _or_ micro version, or minor version zero, indicates that the
resource is a development version.  Hosts and tools SHOULD clearly indicate
this wherever appropriate.  Minor version zero is a special case for
pre-release development of plugins, or experimental plugins that are not
intended for stable use at all.  Hosts SHOULD NOT expect such a plugin to
remain compatible with any future version.  Where feasible, hosts SHOULD NOT
expose such plugins to users by default, but may provide an option to display
them.

"""^^lv2:Markdown .

lv2:microVersion
	lv2:documentation """

Releases of plugins and extensions MUST be explicitly versioned.  Correct
version numbers MUST always be maintained for any versioned resource that is
published. For example, after a release, if a change is made in the development
version in source control, the micro version MUST be incremented (to an odd
number) to distinguish this modified version from the previous release.

This property describes half of a resource version. For detailed documentation
on LV2 resource versioning, see lv2:minorVersion.

"""^^lv2:Markdown .

lv2:binary
	lv2:documentation """

The value of this property must be the URI of a shared library object,
typically in the same bundle as the data file which contains this property.
The actual type of the library is platform specific.

This is a required property of a lv2:Plugin which MUST be included in the
bundle's `manifest.ttl` file.  The lv2:binary of a lv2:Plugin is the shared
object containing the lv2_descriptor() or lv2_lib_descriptor() function.  This
probably may also be used similarly by extensions to relate other resources to
their implementations (it is not implied that a lv2:binary on an arbitrary
resource is an LV2 plugin library).

"""^^lv2:Markdown .

lv2:appliesTo
	lv2:documentation """

This is primarily intended for discovery purposes: bundles that describe
resources that work with particular plugins (like presets or user interfaces)
SHOULD specify this in their `manifest.ttl` so the host can associate them with
the correct plugin.  For example:

    :::turtle
    <thing>
        a             ext:Thing ;
        lv2:appliesTo <plugin> ;
        rdfs:seeAlso  <thing.ttl> .

Using this pattern is preferable for large amounts of data, since the host may
choose whether/when to load the data.

"""^^lv2:Markdown .

lv2:Symbol
	lv2:documentation """

The first character of a symbol must be one of `_`, `a-z` or `A-Z`, and
subsequent characters may additionally be `0-9`.  This is, among other things,
a valid C identifier, and generally compatible in most contexts which have
restrictions on string identifiers, such as file paths.

"""^^lv2:Markdown .

lv2:symbol
	lv2:documentation """

The value of this property MUST be a valid lv2:Symbol, and MUST NOT have a
language tag.

A symbol is a unique identifier with respect to the parent, for example a
port's symbol is a unique identifiers with respect to its plugin.  The plugin
author MUST change the plugin URI if any port symbol is changed or removed.

"""^^lv2:Markdown .

lv2:name
	lv2:documentation """

Unlike lv2:symbol, this is unrestricted, may be translated, and is not relevant
for compatibility.  The name is not necessarily unique and MUST NOT be used as
an identifier.

"""^^lv2:Markdown .

lv2:shortName
	lv2:documentation """

This is the same as lv2:name, with the additional requirement that the value is
shorter than 16 characters.

"""^^lv2:Markdown .

lv2:Designation
	lv2:documentation """

A designation is metadata that describes the meaning or role of something.  By
assigning a designation to a port using lv2:designation, the port's content
becomes meaningful and can be used more intelligently by the host.

"""^^lv2:Markdown .

lv2:Channel
	lv2:documentation """

A specific channel, for example the <q>left</q> channel of a stereo stream.  A
channel may be audio, or another type such as a MIDI control stream.

"""^^lv2:Markdown .

lv2:Parameter
	lv2:documentation """

A parameter is a designation for a control.

A parameter defines the meaning of a control, not the method of conveying its
value.  For example, a parameter could be controlled via a lv2:ControlPort,
messages, or both.

A lv2:ControlPort can be associated with a parameter using lv2:designation.

"""^^lv2:Markdown .

lv2:designation
	lv2:documentation """

This property is used to give a port's contents a well-defined meaning.  For
example, if a port has the designation `eg:gain`, then the value of that port
represents the `eg:gain` of the plugin instance.

Ports should be given designations whenever possible, particularly if a
suitable designation is already defined.  This allows the host to act more
intelligently and provide a more effective user interface.  For example, if the
plugin has a BPM parameter, the host may automatically set that parameter to
the current tempo.

"""^^lv2:Markdown .

lv2:freeWheeling
	lv2:documentation """

If true, this means that all processing is happening as quickly as possible,
not in real-time.  When free-wheeling there is no relationship between the
passage of real wall-clock time and the passage of time in the data being
processed.

"""^^lv2:Markdown .

lv2:enabled
	lv2:documentation """

If this value is greater than zero, the plugin processes normally.  If this
value is zero, the plugin is expected to bypass all signals unmodified.  The
plugin must provide a click-free transition between the enabled and disabled
(bypassed) states.

Values less than zero are reserved for future use (such as click-free
insertion/removal of latent plugins), and should be treated like zero
(bypassed) by current implementations.

"""^^lv2:Markdown .

lv2:control
	lv2:documentation """

This should be used as the lv2:designation of ports that are used to send
commands and receive responses.  Typically this will be an event port that
supports some protocol, for example MIDI or LV2 Atoms.

"""^^lv2:Markdown .

lv2:Point
	lv2:documentation """

  * A Point MUST have at least one rdfs:label which is a string.

  * A Point MUST have exactly one rdf:value with a type that is compatible with
    the type of the corresponding Port.

"""^^lv2:Markdown .

lv2:default
	lv2:documentation """

The host SHOULD set the port to this value initially, and in any situation
where the port value should be cleared or reset.

"""^^lv2:Markdown .

lv2:minimum
	lv2:documentation """

This is a soft limit: the plugin is required to gracefully accept all values in
the range of a port's data type.

"""^^lv2:Markdown .

lv2:maximum
	lv2:documentation """

This is a soft limit: the plugin is required to gracefully accept all values in
the range of a port's data type.

"""^^lv2:Markdown .

lv2:optionalFeature
	lv2:documentation """

To support this feature, the host MUST pass its URI and any additional data to
the plugin in LV2_Descriptor::instantiate().

The plugin MUST NOT fail to instantiate if an optional feature is not supported
by the host.

"""^^lv2:Markdown .

lv2:requiredFeature
	lv2:documentation """

To support this feature, the host MUST pass its URI and any additional data to
the plugin in LV2_Descriptor::instantiate().

The host MUST check this property before attempting to instantiate a plugin,
and not attempt to instantiate plugins which require features it does not
support.  The plugin MUST fail to instantiate if a required feature is not
supported by the host.  Note that these rules are intentionally redundant for
resilience: neither host nor plugin should assume that the other does not
violate them.

"""^^lv2:Markdown .

lv2:ExtensionData
	lv2:documentation """

This is additional data that a plugin may return from
LV2_Descriptor::extension_data().  This is generally used to add APIs to extend
that defined by LV2_Descriptor.

"""^^lv2:Markdown .

lv2:extensionData
	lv2:documentation """

If a plugin has a value for this property, it must be a URI that defines the
extension data.  The plugin should return the appropriate data when
LV2_Descriptor::extension_data() is called with that URI as a parameter.

"""^^lv2:Markdown .

lv2:isLive
	lv2:documentation """

This feature is for plugins that have time-sensitive internals, for example
communicating in real time over a socket.  It indicates to the host that its
input and output must not be cached or subject to significant latency, and that
calls to LV2_Descriptor::run() should be made at a rate that roughly
corresponds to wall clock time (according to the `sample_count` parameter).

Note that this feature is not related to <q>hard real-time</q> execution
requirements (see lv2:hardRTCapable).

"""^^lv2:Markdown .

lv2:inPlaceBroken
	lv2:documentation """

This feature indicates that the plugin may not work correctly if the host
elects to use the same data location for both input and output.  Plugins that
will fail to work correctly if ANY input port is connected to the same location
as ANY output port MUST require this feature.  Doing so should be avoided
whenever possible since it prevents hosts from running the plugin on data
<q>in-place</q>.

"""^^lv2:Markdown .

lv2:hardRTCapable
	lv2:documentation """

This feature indicates that the plugin is capable of running in a <q>hard
real-time</q> environment.  This should be the case for most audio processors,
so most plugins are expected to have this feature.

To support this feature, plugins MUST adhere to the following in all of their
audio class functions (LV2_Descriptor::run() and
LV2_Descriptor::connect_port()):

  * There is no use of `malloc()`, `free()` or any other heap memory management
    functions.

  * There is no use of any library functions which do not adhere to these
    rules.  The plugin may assume that the standard C math library functions
    are safe.

  * There is no access to files, devices, pipes, sockets, system calls, or any
    other mechanism that might result in the process or thread blocking.

  * The maximum amount of time for a `run()` call is bounded by some expression
    of the form `A + B * sample_count`, where `A` and `B` are platform specific
    constants.  Note that this bound does not depend on input signals or plugin
    state.

"""^^lv2:Markdown .

lv2:portProperty
	lv2:documentation """

States that a port has a particular lv2:PortProperty.  This may be ignored
without catastrophic effects, though it may be useful, for example to provide a
sensible user interface for the port.

"""^^lv2:Markdown .

lv2:connectionOptional
	lv2:documentation """

This property means that the port does not have to be connected to valid data
by the host.  To leave a port <q>unconnected</q>, the host MUST explicitly
connect the port to `NULL`.

"""^^lv2:Markdown .

lv2:reportsLatency
	lv2:documentation """

This property indicates that the port is used to express the processing latency
incurred by the plugin, expressed in samples.  The latency may be affected by
the current sample rate, plugin settings, or other factors, and may be changed
by the plugin at any time.  Where the latency is frequency dependent the plugin
may choose any appropriate value.  If a plugin introduces latency it MUST
provide EXACTLY ONE port with this property set.  In <q>fuzzy</q> cases the
value should be the most reasonable one based on user expectation of
input/output alignment.  For example, musical delay plugins should not report
their delay as latency, since it is an intentional effect that the host should
not compensate for.

This property is deprecated, use a lv2:designation of lv2:latency instead,
following the same rules as above:

    :::turtle
	<http://example.org/plugin>
		lv2:port [
			a lv2:OutputPort , lv2:ControlPort ;
			lv2:designation lv2:latency ;
			lv2:symbol "latency" ;
        ]

"""^^lv2:Markdown .

lv2:toggled
	lv2:documentation """

Indicates that the data item should be considered a boolean toggle.  Data less
than or equal to zero should be considered <q>off</q> or <q>false</q>, and data
above zero should be considered <q>on</q> or <q>true</q>.

"""^^lv2:Markdown .

lv2:sampleRate
	lv2:documentation """

Indicates that any specified bounds should be interpreted as multiples of the
sample rate.  For example, a frequency range from 0 Hz to the Nyquist frequency
(half the sample rate) can be specified by using this property with lv2:minimum
0.0 and lv2:maximum 0.5.  Hosts that support bounds at all MUST support this
property.

"""^^lv2:Markdown .

lv2:integer
	lv2:documentation """

Indicates that all the reasonable values for a port are integers.  For such
ports, a user interface should provide a stepped control that only allows
choosing integer values.

Note that this is only a hint, and that the plugin MUST operate reasonably even
if such a port has a non-integer value.

"""^^lv2:Markdown .

lv2:enumeration
	lv2:documentation """

Indicates that all the rasonable values for a port are defined by
lv2:scalePoint properties.  For such ports, a user interface should provide a selector that allows the user to choose any of the scale point values by name.  It is recommended to show the value as well if possible.

Note that this is only a hint, and that the plugin MUST operate reasonably even
if such a port has a value that does not correspond to a scale point.

"""^^lv2:Markdown .

lv2:isSideChain
	lv2:documentation """

Indicates that a port is a <q>sidechain</q>, which affects the output somehow
but should not be considered a part of the main signal chain.  Sidechain ports
SHOULD be lv2:connectionOptional, and may be ignored by hosts.

"""^^lv2:Markdown .

