Can't convert MP4 to MP3 with FFmpeg in Java

I want to extract an audio file(.mp3) from a video file(.3gp) in Android.

Now I'm trying to use ffmpeg in java file, but only to get an broken mp3 file. It only produces a short noise. How can it change to an audio format?

Here is the code I tried.

public void convertToMp3 (String audioFilePath, String soundTitle){

    try {
        //TODO: Grabber
        FrameGrabber grabber = new FFmpegFrameGrabber( audioFilePath ); // 3gpfile
        grabber.setFormat("mp3");
        grabber.setSampleFormat(6);
        grabber.setSampleRate(44100);
        grabber.setFrameRate(30.0);
        grabber.setAudioBitrate(192000);
        grabber.setAudioChannels(2);
        grabber.start();


        //TODO: Recorder
        String stragePath = Environment.getExternalStorageDirectory().getAbsolutePath();
        FrameRecorder recorder = new FFmpegFrameRecorder(stragePath + "/Music/"+soundTitle+".mp3",grabber.getAudioChannels());
        recorder.setSampleFormat(grabber.getSampleFormat());
        recorder.setSampleRate(44100);
        recorder.setSampleFormat(6);
        recorder.setAudioBitrate(128000);
        recorder.setAudioChannels(2);
        recorder.setFormat("mp3");
        recorder.setFrameRate(30.0);
        recorder.setAudioCodec(avcodec.AV_CODEC_ID_MP3);
        recorder.start();


        Frame frame;
        while ((frame = grabber.grabFrame()) != null) {
            recorder.record(frame);
        }
        recorder.stop();
        grabber.stop();

    } catch (FrameGrabber.Exception e) {
        e.printStackTrace();
    } catch (FrameRecorder.Exception e) {
        e.printStackTrace();
    }
}

I used these libraries. Build.Grade(app)

dependencies {
    compile group: 'org.bytedeco', name: 'javacv', version: '0.10'
    compile group: 'org.bytedeco', name: 'javacpp', version: '0.10'
    compile group: 'org.bytedeco.javacpp-presets', name: 'opencv', version: '2.4.9-0.9', classifier: 'android-arm'
    compile group: 'org.bytedeco.javacpp-presets', name: 'ffmpeg', version: '2.3-0.9', classifier: 'android-arm'
}

Do you have any idea? Any advice will be appreciated.