diff --git a/app/src/main/java/com/github/axet/audiorecorder/activities/RecordingActivity.java b/app/src/main/java/com/github/axet/audiorecorder/activities/RecordingActivity.java
index 0435da5..80e5ad8 100644
--- a/app/src/main/java/com/github/axet/audiorecorder/activities/RecordingActivity.java
+++ b/app/src/main/java/com/github/axet/audiorecorder/activities/RecordingActivity.java
@@ -37,16 +37,16 @@ import android.widget.Toast;
 import com.github.axet.audiorecorder.R;
 import com.github.axet.audiorecorder.app.MainApplication;
 import com.github.axet.audiorecorder.app.Storage;
-import com.github.axet.audiorecorder.encoders.FileEncoder;
+import com.github.axet.audiorecorder.encoders.Encoder;
 import com.github.axet.audiorecorder.encoders.EncoderInfo;
-import com.github.axet.audiorecorder.encoders.Wav;
+import com.github.axet.audiorecorder.encoders.FileEncoder;
+import com.github.axet.audiorecorder.encoders.FormatM4A;
+import com.github.axet.audiorecorder.encoders.FormatWAV;
 import com.github.axet.audiorecorder.widgets.PitchView;
 
 import java.io.DataOutputStream;
 import java.io.File;
-import java.io.FileInputStream;
 import java.io.IOException;
-import java.util.concurrent.atomic.AtomicLong;
 
 public class RecordingActivity extends AppCompatActivity {
     public static final String TAG = RecordingActivity.class.getSimpleName();
@@ -551,7 +551,19 @@ public class RecordingActivity extends AppCompatActivity {
 
         EncoderInfo info = getInfo();
 
-        encoder = new FileEncoder(this, in, new Wav(info, out));
+        Encoder e = null;
+
+        SharedPreferences shared = PreferenceManager.getDefaultSharedPreferences(this);
+        String ext = shared.getString(MainApplication.PREFERENCE_ENCODING, "");
+
+        if (ext.equals("wav")) {
+            e = new FormatWAV(info, out);
+        }
+        if (ext.equals("m4a")) {
+            e = new FormatM4A(info, out);
+        }
+
+        encoder = new FileEncoder(this, in, e);
 
         final ProgressDialog d = new ProgressDialog(this);
         d.setTitle("Encoding...");
@@ -564,8 +576,7 @@ public class RecordingActivity extends AppCompatActivity {
         encoder.run(new Runnable() {
             @Override
             public void run() {
-                int i = encoder.getProgress();
-                d.setProgress(i);
+                d.setProgress(encoder.getProgress());
             }
         }, new Runnable() {
             @Override
diff --git a/app/src/main/java/com/github/axet/audiorecorder/activities/SettingsActivity.java b/app/src/main/java/com/github/axet/audiorecorder/activities/SettingsActivity.java
index 04e69db..4629078 100644
--- a/app/src/main/java/com/github/axet/audiorecorder/activities/SettingsActivity.java
+++ b/app/src/main/java/com/github/axet/audiorecorder/activities/SettingsActivity.java
@@ -217,7 +217,15 @@ public class SettingsActivity extends AppCompatPreferenceActivity {
                 bindPreferenceSummaryToValue(findPreference(MainApplication.PREFERENCE_STORAGE));
             }
 
-            bindPreferenceSummaryToValue(findPreference(MainApplication.PREFERENCE_RATE));
+            Preference rate = findPreference(MainApplication.PREFERENCE_RATE);
+
+            if (Build.VERSION.SDK_INT < 21) {
+                getPreferenceScreen().removePreference(rate);
+            } else {
+                bindPreferenceSummaryToValue(rate);
+            }
+
+            bindPreferenceSummaryToValue(findPreference(MainApplication.PREFERENCE_ENCODING));
         }
 
         @Override
diff --git a/app/src/main/java/com/github/axet/audiorecorder/encoders/FileEncoder.java b/app/src/main/java/com/github/axet/audiorecorder/encoders/FileEncoder.java
index 886d13d..3db13e7 100644
--- a/app/src/main/java/com/github/axet/audiorecorder/encoders/FileEncoder.java
+++ b/app/src/main/java/com/github/axet/audiorecorder/encoders/FileEncoder.java
@@ -52,10 +52,10 @@ public class FileEncoder {
 
                         int len = is.read(buf);
                         if (len <= 0) {
+                            Log.d("23", "end");
                             handler.post(done);
                             return;
-                        }
-                        if (len > 0) {
+                        } else {
                             short[] shorts = new short[len / 2];
                             ByteBuffer.wrap(buf, 0, len).order(ByteOrder.BIG_ENDIAN).asShortBuffer().get(shorts);
                             encoder.encode(shorts);
@@ -65,10 +65,13 @@ public class FileEncoder {
                             }
                         }
                     }
+                    Log.d("23", "interrupted " + Thread.currentThread().isInterrupted());
                 } catch (IOException e) {
+                    Log.d("23", "error " + e.getMessage());
                     t = e;
                     handler.post(error);
                 } finally {
+                    Log.d("23", "close");
                     encoder.close();
                     if (is != null) {
                         try {
diff --git a/app/src/main/java/com/github/axet/audiorecorder/encoders/FormatM4A.java b/app/src/main/java/com/github/axet/audiorecorder/encoders/FormatM4A.java
new file mode 100755
index 0000000..513c830
--- /dev/null
+++ b/app/src/main/java/com/github/axet/audiorecorder/encoders/FormatM4A.java
@@ -0,0 +1,112 @@
+package com.github.axet.audiorecorder.encoders;
+
+import android.annotation.TargetApi;
+import android.media.MediaCodec;
+import android.media.MediaCodecInfo;
+import android.media.MediaFormat;
+import android.media.MediaMuxer;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+@TargetApi(21)
+public class FormatM4A implements Encoder {
+    EncoderInfo info;
+    MediaCodec encoder;
+    MediaMuxer muxer;
+    int audioTrackIndex;
+    long NumSamples;
+
+    public FormatM4A() {
+    }
+
+    public FormatM4A(EncoderInfo info, File out) {
+        this.info = info;
+
+        MediaFormat format = new MediaFormat();
+        format.setString(MediaFormat.KEY_MIME, "audio/mp4a-latm");
+        format.setInteger(MediaFormat.KEY_AAC_PROFILE, MediaCodecInfo.CodecProfileLevel.AACObjectHE);
+        format.setInteger(MediaFormat.KEY_SAMPLE_RATE, info.sampleRate);
+        format.setInteger(MediaFormat.KEY_CHANNEL_COUNT, info.channels);
+        format.setInteger(MediaFormat.KEY_BIT_RATE, 128 * 1024);
+
+        try {
+            encoder = MediaCodec.createEncoderByType("audio/mp4a-latm");
+            encoder.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
+            encoder.start();
+
+            muxer = new MediaMuxer(out.getAbsolutePath(), MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public void encode(short[] buf) {
+        int len = buf.length * 2;
+        int inputIndex = encoder.dequeueInputBuffer(-1);
+        if (inputIndex >= 0) {
+            ByteBuffer input = encoder.getInputBuffer(inputIndex);
+            input.clear();
+            for (int i = 0; i < buf.length; i++)
+                input.putShort(buf[i]);
+            encoder.queueInputBuffer(inputIndex, 0, len, getCurrentTimeStamp(), 0);
+        }
+
+        NumSamples += buf.length / info.channels;
+
+        encode();
+    }
+
+    void encode() {
+        MediaCodec.BufferInfo outputInfo = new MediaCodec.BufferInfo();
+        int outputIndex = encoder.dequeueOutputBuffer(outputInfo, 0);
+        if (outputIndex == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
+            audioTrackIndex = muxer.addTrack(encoder.getOutputFormat());
+            muxer.start();
+        }
+
+        while (outputIndex >= 0) {
+            ByteBuffer output = encoder.getOutputBuffer(outputIndex);
+            output.position(outputInfo.offset);
+            output.limit(outputInfo.offset + outputInfo.size);
+
+//            byte[] out = new byte[outputInfo.size];
+//            output.get(out);
+
+            muxer.writeSampleData(audioTrackIndex, output, outputInfo);
+
+            encoder.releaseOutputBuffer(outputIndex, false);
+            outputIndex = encoder.dequeueOutputBuffer(outputInfo, 0);
+        }
+    }
+
+    public void close() {
+        end();
+        encode();
+
+        encoder.stop();
+        encoder.release();
+
+        muxer.stop();
+        muxer.release();
+    }
+
+    long getCurrentTimeStamp() {
+        return NumSamples * 1000 * 1000 / info.sampleRate;
+    }
+
+    void end() {
+        int inputIndex = encoder.dequeueInputBuffer(-1);
+        if (inputIndex >= 0) {
+            ByteBuffer input = encoder.getInputBuffer(inputIndex);
+            input.clear();
+            encoder.queueInputBuffer(inputIndex, 0, 0, getCurrentTimeStamp(), MediaCodec.BUFFER_FLAG_END_OF_STREAM);
+        }
+    }
+
+    public EncoderInfo getInfo() {
+        return info;
+    }
+
+}
\ No newline at end of file
diff --git a/app/src/main/java/com/github/axet/audiorecorder/encoders/Wav.java b/app/src/main/java/com/github/axet/audiorecorder/encoders/FormatWAV.java
similarity index 93%
rename from app/src/main/java/com/github/axet/audiorecorder/encoders/Wav.java
rename to app/src/main/java/com/github/axet/audiorecorder/encoders/FormatWAV.java
index cac5efd..04bf58c 100755
--- a/app/src/main/java/com/github/axet/audiorecorder/encoders/Wav.java
+++ b/app/src/main/java/com/github/axet/audiorecorder/encoders/FormatWAV.java
@@ -8,7 +8,7 @@ import java.io.*;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
-public class Wav implements Encoder {
+public class FormatWAV implements Encoder {
     int NumSamples;
     EncoderInfo info;
     int BytesPerSample;
@@ -16,10 +16,10 @@ public class Wav implements Encoder {
 
     ByteOrder order = ByteOrder.LITTLE_ENDIAN;
 
-    public Wav() {
+    public FormatWAV() {
     }
 
-    public Wav(EncoderInfo info, File out) {
+    public FormatWAV(EncoderInfo info, File out) {
         this.info = info;
         NumSamples = 0;
 
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 3078605..2aa6034 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -23,12 +23,12 @@
 
     <string-array name="encodings" >
         <item>.wav (default)</item>
-        <item>.aac</item>
+        <item>.m4a</item>
     </string-array>
 
     <string-array name="encodings_values" >
         <item>wav</item>
-        <item>aac</item>
+        <item>m4a</item>
     </string-array>
 
     <string name="title_activity_main">Audio Recorder</string>
diff --git a/app/src/main/res/xml/pref_general.xml b/app/src/main/res/xml/pref_general.xml
index 9e72cce..ebbb6e0 100644
--- a/app/src/main/res/xml/pref_general.xml
+++ b/app/src/main/res/xml/pref_general.xml
@@ -22,7 +22,7 @@
         android:key="encoding"
         android:negativeButtonText="@null"
         android:positiveButtonText="@null"
-        android:summary="Output file formats (.wav, .aac, ...)"
+        android:summary="Output file formats (.wav, .m4a, ...)"
         android:title="Encoding" />
 
     <SwitchPreference