Quero criar um aplicativo de gravador de voz, mas ele trava quando clico no botão "Iniciar gravação". Eu recebo um erro dizendo java.lang.IllegalStateException em android.media.MediaRecorder.start (método nativo). Também anexei o log.

package com.example.sahil.chuckit;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.app.Activity;
import android.media.MediaPlayer;
import android.media.MediaRecorder;
import android.os.Environment;
import java.io.File;

public class MainActivity extends Activity {

    private static Button submit;
    private static Button submit2;
    private static Button submit3;
    private static Button submit4;
    private MediaPlayer mediaPlayer;
    private MediaRecorder recorder;
    private String output_file;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        output_file = Environment.getExternalStorageState() +    "/audiorecorder.3gpp";
        OnClickButtonListener();OnClickButtonListener1();
        OnClickButtonListener3();OnClickButtonListener4();
     }
     public void OnClickButtonListener(){
        submit =(Button)findViewById(R.id.button);
        submit.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {

                        beginRecording();

                    }
                    }

        );

    }
    public void OnClickButtonListener1(){
        submit2 =(Button)findViewById(R.id.button2);
        submit2.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        stopRecording();
                    }
                }
        );

    }

    public void OnClickButtonListener3(){
        submit3 =(Button)findViewById(R.id.button3);
        submit3.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        try {
                            playRecording();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                }
        );

    }
    public void OnClickButtonListener4(){
        submit4 =(Button)findViewById(R.id.button4);
        submit4.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                      stopPlayback();
                    }
                }
        );

    }
    private void ditchMediaRecorder() {
        if (recorder != null)
            recorder.release();
    }
    private void beginRecording() {
        ditchMediaRecorder();
        File outFile=new File(output_file);

        if (outFile.exists())
        { outFile.delete();}

        recorder=new MediaRecorder();
        recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
        recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
        recorder.setOutputFile(output_file);
        recorder.start();
    }
    private void stopRecording() {
        if(recorder!=null)
            recorder.stop();
    }

    private void playRecording() throws Exception {
        ditchMediaPlayer();
        mediaPlayer=new MediaPlayer();
        mediaPlayer.setDataSource(output_file);
        mediaPlayer.prepare();
        mediaPlayer.start();
    }

    private void ditchMediaPlayer() {
        if(mediaPlayer!=null)
        {
            try{
                mediaPlayer.release();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    private void stopPlayback() {
        if (mediaPlayer!=null)
            mediaPlayer.stop();
    }




}

Logcat:

LOG:06-30 05:11:12.603 24621-24621/com.example.sahil.chuckit E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.sahil.chuckit, PID: 24621 java.lang.IllegalStateException
    at android.media.MediaRecorder.start(Native Method)
    at com.example.sahil.chuckit.MainActivity.beginRecording(MainActivity.java:111)
    at com.example.sahil.chuckit.MainActivity.access$000(MainActivity.java:22)
    at com.example.sahil.chuckit.MainActivity$1.onClick(MainActivity.java:46)
    at android.view.View.performClick(View.java:5198)
    at android.view.View$PerformClick.run(View.java:21147)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
06-30 05:11:14.891 24621-24621/com.example.sahil.chuckit I/Process: Sending signal. PID: 24621 SIG: 9