annotate vamp-hostsdk/PluginInputDomainAdapter.h @ 288:283e15f6e548

* The beginnings of making the shift-timestamp or shift-data behaviour
  of PluginInputDomainAdapter into an option

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Vamp

    An API for audio analysis and feature extraction plugins.

    Centre for Digital Music, Queen Mary, University of London.
    Copyright 2006-2007 Chris Cannam and QMUL.
  
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*/

#ifndef _VAMP_PLUGIN_INPUT_DOMAIN_ADAPTER_H_
#define _VAMP_PLUGIN_INPUT_DOMAIN_ADAPTER_H_

#include "hostguard.h"
#include "PluginWrapper.h"

_VAMP_SDK_HOSTSPACE_BEGIN(PluginInputDomainAdapter.h)

namespace Vamp {

namespace HostExt {

/**
 * \class PluginInputDomainAdapter PluginInputDomainAdapter.h <vamp-hostsdk/PluginInputDomainAdapter.h>
 * 
 * PluginInputDomainAdapter is a Vamp plugin adapter that converts
 * time-domain input into frequency-domain input for plugins that need
 * it.  This permits a host to use time- and frequency-domain plugins
 * interchangeably without needing to handle the conversion itself.
 *
 * This adapter uses a basic Hanning windowed FFT that supports
 * power-of-two block sizes only.  If a frequency domain plugin
 * requests a non-power-of-two blocksize, the adapter will adjust it
 * to a nearby power of two instead.  Thus, getPreferredBlockSize()
 * will always return a power of two if the wrapped plugin is a
 * frequency domain one.  If the plugin doesn't accept the adjusted
 * power of two block size, initialise() will fail.
 *
 * The adapter provides no way for the host to discover whether the
 * underlying plugin is actually a time or frequency domain plugin
 * (except that if the preferred block size is not a power of two, it
 * must be a time domain plugin).
 *
 * The FFT implementation is simple and self-contained, but unlikely
 * to be the fastest available: a host can usually do better if it
 * cares enough.
 *
 * In every respect other than its input domain handling, the
 * PluginInputDomainAdapter behaves identically to the plugin that it
 * wraps.  The wrapped plugin will be deleted when the wrapper is
 * deleted.
 *
 * \note This class was introduced in version 1.1 of the Vamp plugin SDK.
 */

class PluginInputDomainAdapter : public PluginWrapper
{
public:
    /**
     * Construct a PluginInputDomainAdapter wrapping the given plugin.
     * The adapter takes ownership of the plugin, which will be
     * deleted when the adapter is deleted.
     */
    PluginInputDomainAdapter(Plugin *plugin);
    virtual ~PluginInputDomainAdapter();
    
    bool initialise(size_t channels, size_t stepSize, size_t blockSize);
    void reset();

    InputDomain getInputDomain() const;

    size_t getPreferredStepSize() const;
    size_t getPreferredBlockSize() const;

    FeatureSet process(const float *const *inputBuffers, RealTime timestamp);

    /**
     * ProcessTimestampMethod determines how the
     * PluginInputDomainAdapter handles timestamps for the data passed
     * to the process() function of the plugin it wraps, in the case
     * where the plugin is expecting frequency-domain data.
     *
     *
     * The Vamp API mandates that the timestamp passed to the plugin
     * for time-domain input should be the time of the first sample in
     * the block, but the timestamp passed for frequency-domain input
     * should be the timestamp of the centre of the block.
     *
     * Since we claim to permit the code that uses this plugin wrapper
     * not to care whether the plugin itself has time or frequency
     * domain input, that means that we need to ensure this timestamp
     * is correctly adjusted ourselves, and the way we handle this is
     * controlled by the ProcessTimestampMethod.
     *
     * If ProcessTimestampMethod is ShiftTimestamp (the default), then
     * the data passed to the wrapped plugin will be calculated from
     * the same input data block as passed to the wrapper, but the
     * timestamp passed to the plugin will be advanced by half of the
     * window size.
     * 
     * If ProcessTimestampMethod is ShiftData, then the timestamp
     * passed to the wrapped plugin will be the same as that passed to
     * the process call of the wrapper, but the data block used to
     * calculate the input will be shifted back (earlier) by half of
     * the window size, with half a block of padding at the start of
     * the first process call.
     *
     * This function must be called before the first call to
     * process().
     */
    enum ProcessTimestampMethod {
        ShiftTimestamp,
        ShiftData
    };

    void setProcessTimestampMethod(ProcessTimestampMethod);
    ProcessTimestampMethod getProcessTimestampMethod() const;

    /**
     * Return the amount by which the timestamps supplied to process()
     * are being incremented when they are passed to the plugin's own
     * process() implementation.
     *
     * The Vamp API mandates that the timestamp passed to the plugin
     * for time-domain input should be the time of the first sample in
     * the block, but the timestamp passed for frequency-domain input
     * should be the timestamp of the centre of the block.
     *
     * The PluginInputDomainAdapter adjusts its timestamps properly so
     * that the plugin receives correct times, but in some
     * circumstances (such as for establishing the correct timing of
     * implicitly-timed features, i.e. features without their own
     * timestamps) the host may need to be aware that this adjustment
     * is taking place.
     *
     * If the plugin requires time-domain input or the
     * PluginInputDomainAdapter is configured with its
     * ProcessTimestampMethod set to ShiftData instead of
     * ShiftTimestamp, then this function will return zero.
     *
     * The result of calling this function before initialise() has
     * been called is undefined.
     */
    RealTime getTimestampAdjustment() const;

protected:
    class Impl;
    Impl *m_impl;
};

}

}

_VAMP_SDK_HOSTSPACE_END(PluginInputDomainAdapter.h)

#endif