本文讲述使用Android API MediaProjection 录制手机屏幕
一、实现效果
这个Demo主要是实现Android手机屏幕录制的功能，可以实现视频、音频的录制，可以选取录制视频的效果，是否开启音频录制。截图如下：
点击START按钮开始屏幕录制，这里还可以选择标清或高清视频，是否开启音频录制等；点击STOP按钮结束录制。
二、代码分析
整个Demo比较简单，只有两个类：一个是应用程序入口MainActivity，一个是具体实现录制功能的ScreenRecordService。
在MainActivity中，点击START按钮，系统向用户请求屏幕录制的相关权限，这里获取权限其实是调用 mediaProjectionManager.createScreenCaptureIntent()获得一个intent，通过 startActivityForResult(intent) 请求权限。在onActivityResult() 中响应用户动作，获得允许则开始屏幕录制。代码如下，新建MainActivity继承Activity，向其中加入以下代码：
public class MainActivity extends Activity {
private static final String TAG = "MainActivity";
private TextView mTextView;
private static final String RECORD_STATUS = "record_status";
private static final int REQUEST_CODE = 1000;
private int mScreenWidth;
private int mScreenHeight;
private int mScreenDensity;
/** 是否已经开启视频录制 */
private boolean isStarted = false;
/** 是否为标清视频 */
private boolean isVideoSd = true;
/** 是否开启音频录制 */
private boolean isAudio = true;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.i(TAG, "onCreate");
if(savedInstanceState != null) {
isStarted = savedInstanceState.getBoolean(RECORD_STATUS);
}
getView() ;
getScreenBaseInfo();
}
private void getView() {
mTextView = (TextView) findViewById(R.id.button_control);
if(isStarted) {
statusIsStarted();
} else {
statusIsStoped();
}
mTextView.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if(isStarted) {
stopScreenRecording();
statusIsStoped();
Log.i(TAG, "Stoped screen recording");
} else {
startScreenRecording();
}
}
});
RadioGroup radioGroup = (RadioGroup) findViewById(R.id.radio_group);
radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
// TODO Auto-generated method stub
switch (checkedId) {
case R.id.sd_button:
isVideoSd = true;
break;
case R.id.hd_button:
isVideoSd = false;
break;
default:
break;
}
}
});
CheckBox audioBox = (CheckBox) findViewById(R.id.audio_check_box);
audioBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// TODO Auto-generated method stub
isAudio = isChecked;
}
});
}
/**
* 开启屏幕录制时的UI状态
*/
private void statusIsStarted() {
mTextView.setText(R.string.stop_recording);
mTextView.setBackgroundDrawable(getResources().getDrawable(R.drawable.selector_red_bg));
}
/**
* 结束屏幕录制后的UI状态
*/
private void statusIsStoped() {
mTextView.setText(R.string.start_recording);
mTextView.setBackgroundDrawable(getResources().getDrawable(R.drawable.selector_green_bg));
}
/**
* 获取屏幕相关数据
*/
private void getScreenBaseInfo() {
DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);
mScreenWidth = metrics.widthPixels;
mScreenHeight = metrics.heightPixels;
mScreenDensity = metrics.densityDpi;
}
@Override
protected void onSaveInstanceState(Bundle outState) {
// TODO Auto-generated method stub
super.onSaveInstanceState(outState);
outState.putBoolean(RECORD_STATUS, isStarted);
}
/**
* 获取屏幕录制的权限
*/
private void startScreenRecording() {
// TODO Auto-generated method stub
MediaProjectionManager mediaProjectionManager = (MediaProjectionManager) getSystemService(Context.MEDIA_PROJECTION_SERVICE);
Intent permissionIntent = mediaProjectionManager.createScreenCaptureIntent();
startActivityForResult(permissionIntent, REQUEST_CODE);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if(requestCode == REQUEST_CODE) {
if(resultCode == RESULT_OK) {
// 获得权限，启动Service开始录制
Intent service = new Intent(this, ScreenRecordService.class);
service.putExtra("code", resultCode);
service.putExtra("data", data);
service.putExtra("audio", isAudio);
service.putExtra("width", mScreenWidth);
service.putExtra("height", mScreenHeight);
service.putExtra("density", mScreenDensity);
service.putExtra("quality", isVideoSd);
startService(service);
// 已经开始屏幕录制，修改UI状态
isStarted = !isStarted;
statusIsStarted();
simulateHome(); // this.finish(); // 可以直接关闭Activity
Log.i(TAG, "Started screen recording");
} else {
Toast.makeText(this, R.string.user_cancelled, Toast.LENGTH_LONG).show();
Log.i(TAG, "User cancelled");
}
}
}
/**
* 关闭屏幕录制，即停止录制Service
*/
private void stopScreenRecording() {
// TODO Auto-generated method stub
Intent service = new Intent(this, ScreenRecordService.class);
stopService(service);
isStarted = !isStarted;
}
/**
* 模拟HOME键返回桌面的功能
*/
private void simulateHome() {
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.addCategory(Intent.CATEGORY_HOME);
this.startActivity(intent);
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// 在这里将BACK键模拟了HOME键的返回桌面功能（并无必要）
if(keyCode == KeyEvent.KEYCODE_BACK) {
simulateHome();
return true;
}
return super.onKeyDown(keyCode, event);
}
}
在ScreenRecordService中，第一步需要获得MediaProjectionManager的实例，通过它才可以获得MediaProjection的实例。然后在createMediaRecorder()方法中创建MediaRecorder的实例，并且完成对它的配置。录制的视频的质量就是在这里配置完成的，主要是setVideoEncodingBitRate(), setVideoEncodingBitRate()这两个方法控制。在配置完成后一定要记得mediaRecorder.prepare(); 并且这行代码必须在创建VirtualDisplay的实例之前调用，否则不能正常获取到 Surface的实例。新建类ScreenRecordService继承Service，在其中加入以下代码：
public class ScreenRecordService extends Service {
private static final String TAG = "ScreenRecordingService";
private int mScreenWidth;
private int mScreenHeight;
private int mScreenDensity;
private int mResultCode;
private Intent mResultData;
/** 是否为标清视频 */
private boolean isVideoSd;
/** 是否开启音频录制 */
private boolean isAudio;
private MediaProjection mMediaProjection;
private MediaRecorder mMediaRecorder;
private VirtualDisplay mVirtualDisplay;
@Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();
Log.i(TAG, "Service onCreate() is called");
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// TODO Auto-generated method stub
Log.i(TAG, "Service onStartCommand() is called");
mResultCode = intent.getIntExtra("code", -1);
mResultData = intent.getParcelableExtra("data");
mScreenWidth = intent.getIntExtra("width", 720);
mScreenHeight = intent.getIntExtra("height", 1280);
mScreenDensity = intent.getIntExtra("density", 1);
isVideoSd = intent.getBooleanExtra("quality", true);
isAudio = intent.getBooleanExtra("audio", true);
mMediaProjection = createMediaProjection();
mMediaRecorder = createMediaRecorder();
mVirtualDisplay = createVirtualDisplay(); // 必须在mediaRecorder.prepare() 之后调用，否则报错"fail to get surface"
mMediaRecorder.start();
return Service.START_NOT_STICKY;
}
private MediaProjection createMediaProjection() {
Log.i(TAG, "Create MediaProjection");
return ((MediaProjectionManager) getSystemService(Context.MEDIA_PROJECTION_SERVICE)).getMediaProjection(mResultCode, mResultData);
}
private MediaRecorder createMediaRecorder() {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss");
Date curDate = new Date(System.currentTimeMillis());
String curTime = formatter.format(curDate).replace(" ", "");
String videoQuality = "HD";
if(isVideoSd) videoQuality = "SD";
Log.i(TAG, "Create MediaRecorder");
MediaRecorder mediaRecorder = new MediaRecorder();
if(isAudio) mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
mediaRecorder.setOutputFile(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES) + "/" + videoQuality + curTime + ".mp4");
mediaRecorder.setVideoSize(mScreenWidth, mScreenHeight); //after setVideoSource(), setOutFormat()
mediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264); //after setOutputFormat()
if(isAudio) mediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC); //after setOutputFormat()
int bitRate;
if(isVideoSd) {
mediaRecorder.setVideoEncodingBitRate(mScreenWidth * mScreenHeight);
mediaRecorder.setVideoFrameRate(30);
bitRate = mScreenWidth * mScreenHeight / 1000;
} else {
mediaRecorder.setVideoEncodingBitRate(5 * mScreenWidth * mScreenHeight);
mediaRecorder.setVideoFrameRate(60); //after setVideoSource(), setOutFormat()
bitRate = 5 * mScreenWidth * mScreenHeight / 1000;
}
try {
mediaRecorder.prepare();
} catch (IllegalStateException | IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Log.i(TAG, "Audio: " + isAudio + ", SD video: " + isVideoSd + ", BitRate: " + bitRate + "kbps");
return mediaRecorder;
}
private VirtualDisplay createVirtualDisplay() {
Log.i(TAG, "Create VirtualDisplay");
return mMediaProjection.createVirtualDisplay(TAG, mScreenWidth, mScreenHeight, mScreenDensity,
DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR, mMediaRecorder.getSurface(), null, null);
}
@Override
public void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
Log.i(TAG, "Service onDestroy");
if(mVirtualDisplay != null) {
mVirtualDisplay.release();
mVirtualDisplay = null;
}
if(mMediaRecorder != null) {
mMediaRecorder.setOnErrorListener(null);
mMediaProjection.stop();
mMediaRecorder.reset();
}
if(mMediaProjection != null) {
mMediaProjection.stop();
mMediaProjection = null;
}
}
@Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
return null;
}
}
由上基本就可以实现屏幕录制的功能，但是MediaProjection是在API 21中加入的，所以只能在21以上的手机上使用。在低Android版本的手机上也可以在不root的情况下实现截屏、屏幕录制等功能，但是那都只有应用程序本身占用的屏幕范围，不包括状态栏。最后记得在manifest.xml中加入以下权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
如果你的项目中并不需要录制音频，则 "android.permission.RECORD_AUDIO" 这句可以不要。这里录制的音频只能是来自麦克风的声音，并不能直接录制手机发出的声音，比如电话录音等。
三、补充与总结
屏幕录制的步骤大概可以总结为：1）通过MediaProjectionManager取得向用户申请权限的intent，在onActivityResult()完成对用户动作的响应；2）用户允许后开始录制，可以直接写在一个Activity里，但是像这样另外写在Service里更为妥当，录制的代码也可以单独抽出来写成一个ScreenRecorder的类；3）获取MediaProjection的实例，获取及配置MediaRecorder的实例，并记得MediaRecorder需要prepare()；4）获取VirtualDisplay的实例，它也是MediaProjection, MediaRecorder完成交互的地方，录制的屏幕内容其实就是mediaRecorder.getSurface() 获得的 surface 上的内容。
如果不使用MediaProjection + MediaRecorder组合，也可以使用MediaProjection + MediaCodec + MediaMuxer组合实现相同的功能。其中各个类的作用简要总结如下：
MediaMuxer:将音频和视频进行混合生成多媒体文件，输出mp4格式；
MediaCodec：将音视频进行压缩编码，并可以对Surface内容进行编码，实现屏幕录像功能；
MediaExtrator:将音视频分路，和MediaCodec正好反过程；
MediaFormat：用于描述多媒体数据的格式；
MediaRecoder:用于录像并压缩编码，相较于MediaCodec更适合屏幕录像；
MediaPlayer:用于播放压缩编码后的音视频文件；
AudioRecord:用于录制PCM数据；
AudioTrack:用于播放PCM数据； PCM即原始音频采样数据
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