- libsndfile for opening and reading the wav file
- libportaudio for audio playback
- FFTW3 for performing the FFT of each chunk of audio stream
- libboost for IPC

typedef struct FFTW_Point {
    int x_val;
    float y_val;
} FFTW_Point;

static int pa_callback(
    const void                     *input,
    void                           *output,
    unsigned long                   frameCount,
    const PaStreamCallbackTimeInfo *timeInfo,
    PaStreamCallbackFlags           statusFlags,
    void                           *userData
) {
    float           *out;
    snd_data *p_data = (snd_data*)userData;
    sf_count_t       num_read;

    out = (float*)output;
    p_data = (snd_data*)userData;

    memset(out, 0, sizeof(float) * frameCount * p_data->info.channels);
    num_read = sf_read_float(p_data->file, out, frameCount * p_data->info.channels);

    if ((long unsigned int) num_read < frameCount)
    {
        fftw->setNumSamples(num_read);
        fftw->loadInputData(out);
        //fftw->writeWav();
        return paComplete;
    }
    fftw->loadInputData(out);
    return paContinue;
}

inline static double hannWindow(float value, int i, unsigned int size) {
    return value * (0.5 * (1 - cos(2*M_PI*i/(size))));
}

void FFTW_Tool::loadInputData(float* buffer) {
    for (size_t i = 0; i < numSamples; ++i) {
        in[i][0] = hannWindow(buffer[i], i, numSamples);
        in[i][1] = 0;
    }
    StartFFTW();
}

void FFTW_Tool::executePlan(const unsigned int numSamples,
    const int direction,
    const unsigned int calculationType) {

    fftw_plan plan = fftw_plan_dft_1d(
        numSamples,
        in,
        out,
        direction,
        calculationType
    );

    fftw_execute(plan);
    //shm_region.flush();
    //outputSize = numSamples/2
    for (size_t i = 0; i < outputSize; ++i) {
        sharedStruct[i].x_val = i * samplingFreq / numSamples;
        auto real = out[i][0];
        auto img = out[i][1];
        auto mag = complexModule(real, img);
        auto amp = (2*mag)/numSamples;
        sharedStruct[i].y_val = amp;
    }

    fftw_destroy_plan(plan);
    std::memcpy(shm_region.get_address(), sharedStruct, (sizeof(FFTW_Point) * outputSize));

}

def update(self):
        shmem = mmap.mmap(fd, 0, access=mmap.ACCESS_READ)
        xs = []
        ys = []
        for i1, i2, i3, i4, f1, f2, f3, f4 in zip(*[iter(shmem)]*8):
            x_val = struct.unpack('i', i1+i2+i3+i4)[0]
            y_val = struct.unpack('f', f1+f2+f3+f4)[0]
            xs.append(x_val)
            ys.append(20*np.log10(y_val))
            #ys.append(y_val)
        self.set_plotdata(name='spectrum', data_x=xs, data_y=ys)