Sensor Fun: Creating a simple audio recorder/player

Sound recording and playback is really simple using the MediaRecorder and MediaPlayer classes .. see the example below ..

Sample App

First some layout .. a button to start/stop recording and a button to play the recorded stuff (main.xml):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView
	android:id="@+id/output"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text=""
    />
<Button android:text="@+string/record" android:id="@+id/btRecord" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
<Button android:text="@+string/play" android:id="@+id/btPlay" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
</LinearLayout>

Adjusting the externalized strings in the strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">Soundrecorder Tutorial</string>
	<string name="record">Record!</string>
	<string name="play">Play</string>
</resources>

Set permissions needed in the AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.hascode.android"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".RecorderActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
    <uses-sdk android:minSdkVersion="7" />

<uses-permission android:name="android.permission.RECORD_AUDIO"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
</manifest>

Now the activity to bring in some action .. RecorderActivity.java

package com.hascode.android;

import java.io.File;
import java.io.IOException;

import android.app.Activity;
import android.media.MediaPlayer;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class RecorderActivity extends Activity {
	private static final String APP_TAG = "com.hascode.android.soundrecorder";

	private MediaRecorder recorder = new MediaRecorder();
	private MediaPlayer player = new MediaPlayer();

	private Button btRecord;
	private Button btPlay;
	private TextView resultView;

	private boolean recording = false;
	private boolean playing = false;
	private File outfile = null;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		resultView = (TextView) findViewById(R.id.output);

		try {
			// the soundfile
			File storageDir = new File(Environment
					.getExternalStorageDirectory(), "com.hascode.recorder");
			storageDir.mkdir();
			Log.d(APP_TAG, "Storage directory set to " + storageDir);
			outfile = File.createTempFile("hascode", ".3gp", storageDir);

			// init recorder
			recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
			recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
			recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
			recorder.setOutputFile(outfile.getAbsolutePath());

			// init player
			player.setDataSource(outfile.getAbsolutePath());
		} catch (IOException e) {
			Log.w(APP_TAG, "File not accessible ", e);
		} catch (IllegalArgumentException e) {
			Log.w(APP_TAG, "Illegal argument ", e);
		} catch (IllegalStateException e) {
			Log.w(APP_TAG, "Illegal state, call reset/restore", e);
		}

		btRecord = (Button) findViewById(R.id.btRecord);
		btRecord.setOnClickListener(handleRecordClick);

		btPlay = (Button) findViewById(R.id.btPlay);
		btPlay.setOnClickListener(handlePlayClick);

	}

	private final OnClickListener handleRecordClick = new OnClickListener() {
		@Override
		public void onClick(View view) {
			if (!recording) {
				startRecord();
			} else {
				stopRecord();
			}
		}
	};

	private final OnClickListener handlePlayClick = new OnClickListener() {
		@Override
		public void onClick(View view) {
			if (!playing) {
				startPlay();
			} else {
				stopPlay();
			}
		}
	};

	private void startRecord() {
		Log.d(APP_TAG, "start recording..");
		printResult("start recording..");
		try {
			recorder.prepare();
			recorder.start();
			recording = true;
		} catch (IllegalStateException e) {
			Log
					.w(APP_TAG,
							"Invalid recorder state .. reset/release should have been called");
		} catch (IOException e) {
			Log.w(APP_TAG, "Could not write to sd card");
		}
	}

	private void stopRecord() {
		Log.d(APP_TAG, "stop recording..");
		printResult("stop recording..");
		recorder.stop();
		recorder.reset();
		recorder.release();
		recording = false;
	}

	private void startPlay() {
		Log.d(APP_TAG, "starting playback..");
		printResult("start playing..");
		try {
			playing = true;
			player.prepare();
			player.start();
		} catch (IllegalStateException e) {
			Log.w(APP_TAG, "illegal state .. player should be reset");
		} catch (IOException e) {
			Log.w(APP_TAG, "Could not write to sd card");
		}
	}

	private void stopPlay() {
		Log.d(APP_TAG, "stopping playback..");
		printResult("stop playing..");
		player.stop();
		player.reset();
		player.release();
		playing = false;
	}

	private void printResult(String result) {
		resultView.setText(result);
	}
}

Finally the app looks like this on my emulator

The Application in the Android Emulator
Now play around with the recorder

How to connect a virtual sdcard to the emulator

A SD Card is created using the android tool or the mksdcard tool

android create avd -n <youravd> -t <targetID> -c <size>[K|M]
or:
mksdcard <size> <file>

Start the emulator with the param -sdcard /path/to/sdcard.img
More information is available at the Android Developers Website

Troubleshooting

In general use the logcat tool from the Android Debugging Bridge to look for debugging messages, exceptions, strack traces ..

# adb -s emulator-5554 shell
logcat
I/ActivityManager(   52): Displayed activity com.hascode.android/.RecorderActivity:
I/ARMAssembler(   52): generated scanline__00000077:03545404_00000A04_00000000 [ 29
I/ARMAssembler(   52): generated scanline__00000177:03515104_00001A01_00000000 [ 73
D/com.hascode.android.soundrecorder(  198): start recording..
W/com.hascode.android.soundrecorder(  198): Could not write to sd card

W/com.hascode.android.soundrecorder(209): File not accessible – Check the permissions set for the directory you are trying to save the files to – more information is available at the Android Developers Website – also take a look in your AndroidManifest.xml and check if the permission WRITE_EXTERNAL_STORAGE is set:
```
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
```

Using the Android Debugging Bridge it is possible to check the user permissions set in the emulator

adb -s emulator-5554 shell
# ls -l sdcard
d---rwxr-x system   sdcard_rw          2010-05-02 14:50 LOST.DIR
# ls -l sdcard/com.hascode.recorder
----rwxr-x system   sdcard_rw        0 2010-05-02 15:33 hascode44433.3gp

If you need a GUI – try the the Dalvik Debug Monitor Service by running ddms – screenshots below:

Figure 1. Debugging in DDMS

Figure 2. File System

Resources

Article Updates

2015-03-03: Table of contents and image captions added.

Sample App#

How to connect a virtual sdcard to the emulator#

Troubleshooting#

Resources#

Article Updates#

Sample App

How to connect a virtual sdcard to the emulator

Troubleshooting

Resources

Article Updates