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Editorial Team
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Asked: 2026-06-08T16:04:18+00:00

I build Android project where I use Android NDK with LibXTract to extract audio

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I build Android project where I use Android NDK with LibXTract to extract audio features. LibXTract use fftw3 library. Project is consisted of button which runs simple example form libxtract:

JNIEXPORT void JNICALL Java_com_androidnative1_NativeClass_showText(JNIEnv *env, jclass clazz)
{
    float mean = 0, vector[] = {.1, .2, .3, .4, -.5, -.4, -.3, -.2, -.1}, spectrum[10];
    int n, N = 9;
    float argf[4];

    argf[0] = 8000.f;
    argf[1] = XTRACT_MAGNITUDE_SPECTRUM;
    argf[2] = 0.f;
    argf[3] = 0.f;

    xtract[XTRACT_MEAN]((void *)&vector, N, 0, (void *)&mean);
    __android_log_print(ANDROID_LOG_DEBUG, "AndNat", "com_androidnative1_NativeClass.c before");
    xtract_init_fft(N, XTRACT_SPECTRUM);
    __android_log_print(ANDROID_LOG_DEBUG, "AndNat", "com_androidnative1_NativeClass.c after");
    // Comment for test purpose
    //xtract_init_bark(1, argf[1], 1);
    //xtract[XTRACT_SPECTRUM]((void *)&vector, N, &argf[0], (void *)&spectrum[0]);
}

Libxtract function xtract_init_fft locate in jni/libxtract/jni/src/init.c execute fftw3 function fftwf_plan_r2r_1d located at jni/fftw3/jni/api/plan-r2r-1d.c

__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "libxtract/src/init.c before");
fft_plans.spectrum_plan = fftwf_plan_r2r_1d(N, input, output, FFTW_R2HC, optimisation);
__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "libxtract/src/init.c after");

Application hang inside fftwf_paln_r2r_1d without crash or any outher error I must force it to stop working.

fftwf_paln_r2r_1d looks like:

X(plan) X(plan_r2r_1d)(int n, R *in, R *out, X(r2r_kind) kind, unsigned flags)
{
    __android_log_print(ANDROID_LOG_DEBUG, "AndNat", "fftw3/api/plan-r2r-1d.c");
    return X(plan_r2r)(1, &n, in, out, &kind, flags);
}

From CatLog I can see:

07-16 18:50:09.615: D/AndNat(7313): com_androidnative1_NativeClass.c before
07-16 18:50:09.615: D/AndNat(7313): libxtract/src/init.c before
07-16 18:50:09.615: D/AndNat(7313): fftw3/api/plan-r2r-1d.c

I genereate config.h for fftw3 and libxtract with gen.sh scripts locate in source folder with success. Both librearies are build as static and linked with shared libary libcom_androidnative1_NativeClass.so

Command 

nm -Ca libcom_androidnative1_NativeClass.so

shows that used function is included.

Application is built and deploys to device without any problems.

I build fftw3 with flags –disable-alloca, –enable-float and LibXTract with flags –enable-fft and –disable-dependency-tracking

Only ingerention in library source code was added dbgprint and remove define XTRACT_FFT form LibXtract beacouse it can’t detect fftw library.

If somebody have any idea about this strange for me behavior please help.

Here I put entire project in github so maybe someone can help me handle this.

https://github.com/bl0ndynek/AndroidNative1

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1 Answer

  1. Editorial Team

    Thanks for FFTW3 maintainer problem is solved.
    Solution was to change optimization level from FFTW_MEASURE to FFTW_ESTIMATE (from 1 to 0) in FFTW3,
    FFTW’s planner (in xtract_init_fft) actually executes and times different possible FFT algorithms in order to pick the fastest plan for a given n. In order to do this in as short a time as possible, however, the timer must have a very high resolution, and to accomplish this FFTW3 employ the hardware cycle counters that are available on most CPUs but not on Android default ARM configuration.
    So this algorithm use gettimeofday() witch have low resolution and on ARM took forever on xtract_init_fft.

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