PiPo — Plugin Interface for Processing Objects
PiPo is an extremely simple plugin API for modules processing streams of multi-dimensional data such as audio, audio descriptors, or gesture and motion data. The current version of the interface is limited to unary operations. Each PiPo module receives and produces a single stream. The elements of a stream are time-tagged or regularly sampled scalars, vectors, or two-dimensional matrices.
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PiPo has been developed to be make things simple for users and developers.
User Level Features
- Easy integration and customization of stream processing modules
- Suited for filtering, transformation, extraction, and segmentation algorithms
- Real-time and offline processing
- Applying to audio and control streams (for whom this distinction still makes sense)
Developer Level Features
- Fast and easy implementation of modules and reuse of code for different contexts
- C/C++ API defined by a single header file without additional dependencies
- Core API as single abstract class defining a small set of virtual methods
PiPo Stream Attributes
PiPo streams are a sequences of frames characterized by a set of attributes. A PiPo module defines the attributes of its output stream when receiving the attributes of the input stream.
Each module can configure its internal state depending on the attributes of the input stream (e.g. memory allocation and pre-calculated state variables) before propagating its output stream attributes to the next module.
This way, the attributes of the input stream are propagated through a series of PiPo modules before starting the actual stream processing.
In summary, a PiPo stream is described by the following attributes:
- a boolean representing whether the elements of the stream are time-tagged
- frame rate (highest average rate for time-tagged streams)
- lag of the output stream relative to the input
- frame width (also number of channels or matrix columns)
- frame size (or number of matrix rows)
- labels (for the frame channels or columns)
- a boolean representing whether the frames have a variable size (respecting the given frame size as maximum)
- extent of a frame in the given domain (e.g. duration or frequency range)
- maximum number of frames in a block exchanged between two modules
PiPo Module Parameters
The PiPo SDK comes with a template class PiPo::Attr permits to define scalar, enum, or variable or fixed size vector attributes of a pipo module that are exposed to the host environment.
Since certain parameter changes may also change the attributes of a module’s output stream, PiPo provides a mechanism for signaling these changes through the following modules to the processing environment (i.e. the PiPo host).
For MAX/MSP PiPo includes a binding to extend a PiPo class to a Max/MSP external that then declares the module's parameters as Max/MSP attributes and implement the required setters and getters.
The PiPo Module API consists of the abstract class PiPo in PiPo.h of a few virtual methods for propagating stream attributes (see above), frames, and additional processing control through a series of modules:
- Propagating stream attributes
- Propagating frames
- Reset stream processing
- Finalize stream processing
- Propagate the change of a parameter requiring redefining the output stream attributes
See the doc extraced from PiPo.h at: http://recherche.ircam.fr/equipes/temps-reel/mubu/pipo/sdk-doc-v0.1/
Classes supporting implementation of PiPo hosts are found in directory host.