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audioinput.h Example File
multimedia/audio/audioinput/audioinput.h

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 #include <QPixmap>
 #include <QWidget>
 #include <QObject>
 #include <QMainWindow>
 #include <QPushButton>
 #include <QComboBox>

 #include <qaudioinput.h>

 #define BUFFER_SIZE_LOG 9
 #define BUFFER_SIZE (1 << BUFFER_SIZE_LOG)

 struct _struct_fft_state {
     float real[BUFFER_SIZE];
     float imag[BUFFER_SIZE];
 };
 typedef _struct_fft_state   fft_state;
 typedef short int           sound_sample;

 class Spectrum : public QIODevice
 {
     Q_OBJECT
 public:
     Spectrum(QObject* parent, QAudioInput* device, float* out);
     ~Spectrum();

     void start();
     void stop();

     qint64 readData(char *data, qint64 maxlen);
     qint64 writeData(const char *data, qint64 len);

     QAudioInput*   input;
     float*         output;
     fft_state*     fftState;

     unsigned int bitReverse[BUFFER_SIZE];
     float        sintable[BUFFER_SIZE / 2];
     float        costable[BUFFER_SIZE / 2];

     void prepFFT (const sound_sample *input, float *re, float *im);
     void calcFFT (float *re, float *im);
     void outputFFT (const float *re, const float *im);
     int  reverseBits (unsigned int initial);
     void performFFT (const sound_sample *input);

 signals:
     void update();
 };

 class RenderArea : public QWidget
 {
     Q_OBJECT

 public:
     RenderArea(QWidget *parent = 0);

     void spectrum(float* output, int size);

 protected:
     void paintEvent(QPaintEvent *event);

 private:
     QPixmap pixmap;

     float*  samples;
     int     sampleSize;
 };

 class InputTest : public QMainWindow
 {
     Q_OBJECT
 public:
     InputTest();
     ~InputTest();

     QAudioDeviceId device;
     QAudioFormat   format;
     QAudioInput*   audioInput;
     Spectrum*      spec;
     QIODevice*     input;
     RenderArea*    canvas;

     bool           pullMode;

     QPushButton*   button;
     QPushButton*   button2;
     QComboBox*     deviceBox;

     char*          buffer;
     float*         output;

 private slots:
     void refreshDisplay();
     void status();
     void readMore();
     void toggleMode();
     void toggleSuspend();
     void state(QAudio::State s);
     void deviceChanged(int idx);
 };