Android 4.4中AudioRecord用例 - 录制系统内置声音

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。


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