Android 4.4中AudioRecord用例

通过API 19新加的MediaRecorder.AudioSource.REMOTE_SUBMIX參数能够让系统App录制系统内置的声音，也就是扬声器的声音。以下是一个巨简单的样例来演示样例怎样通过AudioRecord配合REMOTE_SUBMIX參数进行录制。

1. 编译apk

MainActivity.java：

package com.example.audiotest;

import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {
	private static String TAG = "JZJ";
	AudioRecord mRecord = null;
	boolean mReqStop = false;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		init();
		(new Thread() {
			@Override
			public void run() {
				recordAndPlay();
			}
		}).start();
	}

	private final int kSampleRate = 44100;
	private final int kChannelMode = AudioFormat.CHANNEL_IN_STEREO;
	private final int kEncodeFormat = AudioFormat.ENCODING_PCM_16BIT;

	private void init() {
		int minBufferSize = AudioRecord.getMinBufferSize(kSampleRate, kChannelMode,
				kEncodeFormat);
		mRecord = new AudioRecord(MediaRecorder.AudioSource.REMOTE_SUBMIX,
				kSampleRate, kChannelMode, kEncodeFormat, minBufferSize * 2);
	}

	private final int kFrameSize = 2048;
	private String filePath = "/sdcard/voice.pcm";

	private void recordAndPlay() {
		FileOutputStream os = null;
		mRecord.startRecording();
		try {
			os = new FileOutputStream(filePath);
			byte[] buffer = new byte[kFrameSize];
			int num = 0;
			while (!mReqStop) {
				num = mRecord.read(buffer, 0, kFrameSize);
				Log.d(TAG, "buffer = " + buffer.toString() + ", num = " + num);
				os.write(buffer, 0, num);
			}

			Log.d(TAG, "exit loop");
			os.close();
		} catch (IOException e) {
			e.printStackTrace();
			Log.e(TAG, "Dump PCM to file failed");
		}
		mRecord.stop();
		mRecord.release();
		mRecord = null;
		Log.d(TAG, "clean up");
	}

	public void stop(View view) {
		mReqStop = true;
		Button stopBtn = (Button) findViewById(R.id.stopBtn);
		stopBtn.setText("Stopped");
		stopBtn.setEnabled(false);
	}
}

布局文件activity_main.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/stopBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="stop"
        android:text="Stop" />

</RelativeLayout>

配置文件AndroidManifest.xml，注意要加上的几个权限：

<?xml version="1.0" encoding="utf-8"?
>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.audiotest"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-permission android:name="android.permission.CAPTURE_AUDIO_OUTPUT" />
    <uses-permission android:name="android.permission.CAPTURE_VIDEO_OUTPUT"/>
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-sdk
        android:minSdkVersion="19"
        android:targetSdkVersion="19" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.audiotest.MainActivity"
            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>

</manifest>

编译生成Test.apk。

2. 加系统签名

java -jar signapk.jar platform.x509.pem platform.pk8 ./Test.apk final.apk

platform.x509.pem和platform.pk8在Android源代码的build/target/product/security文件夹下。

signapk.jar能够从https://code.google.com/p/signapk/下载。

3. 安装签名好的apk，执行

启动时即開始採集系统声音数据，结束时点击Stopbutton停止。这时採集数据会导出到/sdcard/voice.pcm文件。

4. 取出音频採样数据，播放

adb pull /sdcard/voice.pcm 

vlc --demux=rawaud --rawaud-channels 2 --rawaud-samplerate 44100 voice.pcm

这样就開始播放刚才录制的声音了。vlc是一个多媒体播放器（http://www.videolan.org/vlc/index.html）。支持播放PCM数据。当然也能够用其他支持播放PCM的播放器。

总结来说。这样的方法的缺点是录制时扬声器就不能输出，长处是不用改系统层。假设要两个同一时候输出能够參考这篇文章：http://xzpeter.org/?p=254。