FEAPI Plugin Documentation

Introduction

This is a short tutorial on how to implement a plugin conforming to the Feature Extraction plugin API.
Although the plugin interface is in the C language, the plugin SDK internals are in C++ to ensure API conformance with minimal implementation effort.

Step-by-step tutorial

For the implementation, you need the following SDK files:

• FEAPI.h: the plugin API interface itself (do never edit!)
• FEAPIPluginBase.h: the plugin base class interface (do never edit!)
• FEAPIPluginBase.cpp: prototype implementation of "internal" API functions (do never edit!)
• FEAPIEntryPoints.h: the definition of the API functions (do never edit!)

To make each step more transparent, please refer to the source code of an example plugin (e.g. FindAbsoluteMax).

The following steps are necessary:

• add the above files to your project to build a shared library
• add a new class that is inherited from the class CFeatureExtractBase defined in FEAPIPluginBase.h; let's assume your class is named CMyPlug, its interface is in MyPlug.h and its implementation is in MyPlug.cpp
• do not forget to add the following lines to the beginning of MyPlug.cpp:

      #include "FEAPI.h"
      #include "MyPlug.h"    
      #include "FEAPIEntryPoints.h"
  

• and at the end of file MyPlug.cpp, add the following code

      // entry points
      #ifdef __cplusplus                                                      
      extern "C" {                                                            
      #endif                                                              
      
      FEAPI_ENTRY_POINTS(CMyPlug) // insert your class name here
      
      #ifdef __cplusplus                                                  
      }                                                               
      #endif
      ///////////////////////////////////////
  

• in the interface and implementation of CMyPlug, declare and implement at least all pure virtual functions from the base class

After these steps, your plugin compiles, but does nothing other than just return the default values on all method calls. To change this behaviour, the methods inherited from CFEAPIBase have to be implemented in your class.

Pure virtual base class methods

To get a working plugin, at least the following methods need to be implemented (for detailed documentation, please refer to the "FEAPI Documentation":

• CFeatureExtractBase::GetPluginProperty (FEAPI_PluginProperty_t ePluginProperty)
• CFeatureExtractBase::ProcessPlugin (const FEAPI_Signal_t **ppfInputBuffer, const FEAPI_TimeStamp_t *ptFEAPI_TimeStamp, int iNumberOfFrames)
• CFeatureExtractBase::GetPluginSizeOfResult (int iResultIndex)
• CFeatureExtractBase::GetPluginResult (int iResultIndex, float *pfResult, FEAPI_TimeStamp_t *ptFEAPI_TimeStamp)

Other virtual base class methods

For implementing a real-world plugin, you will most probably need to override the following methods as well:

• CFeatureExtractBase::SetPluginParameter (int iParameterIndex, float fValue)
• CFeatureExtractBase::GetPluginParameter (int iParameterIndex)

Setting input, result and parameter descriptions

To ensure that your plugin returns all descriptions, either for inputs, parameters or results, make sure that you make use of the CPin class, in particular its CPin::SetDescription function to properly set these descriptions.

Contact

web: http://feapi.sourceforge.net
feapi mailing list: feapi-discussion@lists.sourceforge.net

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