我想写一个通过智能手机相机录制视频的应用程序。我找到了这个网站寻求帮助：http://developer.android.com/guide/topics/media/camera.html#custom-camera
即时使用该源代码开始。
我的主要活动：
public class MainActivity extends Activity {
protected static final String TAG = null;
private Camera mCamera;
private CameraPreview mPreview;
private MediaRecorder mMediaRecorder=null;
public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;
private boolean isRecording = false;
/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
}
catch (Exception e){
// Camera is not available (in use or does not exist)
}
return c; // returns null if camera is unavailable
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create an instance of Camera
mCamera = getCameraInstance();
// Create our Preview view and set it as the content of our activity.
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
// Add a listener to the Capture button
final Button captureButton = (Button) findViewById(R.id.button_capture);
captureButton.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
if (isRecording) {
// stop recording and release camera
mMediaRecorder.stop(); // stop the recording
releaseMediaRecorder(); // release the MediaRecorder object
mCamera.lock(); // take camera access back from MediaRecorder
// inform the user that recording has stopped
captureButton.setText("Capture");
//setCaptureButtonText("Capture");
isRecording = false;
} else {
// initialize video camera
if (prepareVideoRecorder()) {
// Camera is available and unlocked, MediaRecorder is prepared,
// now you can start recording
mMediaRecorder.start();
// inform the user that recording has started
captureButton.setText("Stop");
//setCaptureButtonText("Stop");
isRecording = true;
} else {
// prepare didn't work, release the camera
releaseMediaRecorder();
// inform user
}
}
}
}
);
}
@SuppressLint("NewApi") private boolean prepareVideoRecorder(){
mCamera = getCameraInstance();
Log.d(TAG, "mcamera object: " + mCamera.getNumberOfCameras());
mMediaRecorder = new MediaRecorder();
// Step 1: Unlock and set camera to MediaRecorder
try{
mCamera.unlock();
}catch (RuntimeException r){
Log.d(TAG, "mcamera unlock: " + r.getMessage());
}
mMediaRecorder.setCamera(mCamera);
// Step 2: Set sources
mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA);
// Step 3: Set a CamcorderProfile (requires API Level 8 or higher)
mMediaRecorder.setProfile(CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH));
// Step 4: Set output file
mMediaRecorder.setOutputFile(getOutputMediaFile(MEDIA_TYPE_VIDEO).toString());
// Step 5: Set the preview output
mMediaRecorder.setPreviewDisplay(mPreview.getHolder().getSurface());
// Step 6: Prepare configured MediaRecorder
try {
mMediaRecorder.prepare();
} catch (IllegalStateException e) {
Log.d(TAG, "IllegalStateException preparing MediaRecorder: " + e.getMessage());
releaseMediaRecorder();
return false;
} catch (IOException e) {
Log.d(TAG, "IOException preparing MediaRecorder: " + e.getMessage());
releaseMediaRecorder();
return false;
}
return true;
}
@Override
protected void onPause() {
super.onPause();
releaseMediaRecorder(); // if you are using MediaRecorder, release it first
releaseCamera(); // release the camera immediately on pause event
}
private void releaseMediaRecorder(){
if (mMediaRecorder != null) {
mMediaRecorder.reset(); // clear recorder configuration
mMediaRecorder.release(); // release the recorder object
mMediaRecorder = null;
mCamera.lock(); // lock camera for later use
}
}
private void releaseCamera(){
if (mCamera != null){
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
/** Create a File for saving an image or video */
private static File getOutputMediaFile(int type){
// To be safe, you should check that the SDCard is mounted
// using Environment.getExternalStorageState() before doing this.
File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_PICTURES), "MyCameraApp");
// This location works best if you want the created images to be shared
// between applications and persist after your app has been uninstalled.
// Create the storage directory if it does not exist
if (! mediaStorageDir.exists()){
if (! mediaStorageDir.mkdirs()){
Log.d("MyCameraApp", "failed to create directory");
return null;
}
}
// Create a media file name
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
File mediaFile;
if (type == MEDIA_TYPE_IMAGE){
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"IMG_"+ timeStamp + ".jpg");
} else if(type == MEDIA_TYPE_VIDEO) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"VID_"+ timeStamp + ".mp4");
} else {
return null;
}
return mediaFile;
}
}
我的相机预览课程：
/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private static final String TAG = "Preview";
public CameraPreview(Context context, Camera camera) {
super(context);
mCamera = camera;
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
// deprecated setting, but required on Android versions prior to 3.0
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, now tell the camera where to draw the preview.
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
// empty. Take care of releasing the Camera preview in your activity.
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
if (mHolder.getSurface() == null){
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e){
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
// start preview with new settings
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
}
但是当我在我的samsung s5660 API 2.3.3上运行应用程序时，我收到此错误：
06-07 19:55:48.859: D/(20274): mcamera object: 1
06-07 21:10:19.159: D/(20465): mcamera unlock: null
06-07 19:55:48.859: W/dalvikvm(20274): threadid=1: thread exiting with uncaught exception (group=0x40018578)
06-07 19:55:48.859: E/AndroidRuntime(20274): FATAL EXCEPTION: main
06-07 19:55:48.859: E/AndroidRuntime(20274): java.lang.NullPointerException
06-07 19:55:48.859: E/AndroidRuntime(20274): at com.example.videocapture.MainActivity.prepareVideoRecorder(MainActivity.java:118)
06-07 19:55:48.859: E/AndroidRuntime(20274): at com.example.videocapture.MainActivity.access$5(MainActivity.java:111)
06-07 19:55:48.859: E/AndroidRuntime(20274): at com.example.videocapture.MainActivity$1.onClick(MainActivity.java:91)
06-07 19:55:48.859: E/AndroidRuntime(20274): at android.view.View.performClick(View.java:2485)
06-07 19:55:48.859: E/AndroidRuntime(20274): at android.view.View$PerformClick.run(View.java:9080)
06-07 19:55:48.859: E/AndroidRuntime(20274): at android.os.Handler.handleCallback(Handler.java:587)
06-07 19:55:48.859: E/AndroidRuntime(20274): at android.os.Handler.dispatchMessage(Handler.java:92)
06-07 19:55:48.859: E/AndroidRuntime(20274): at android.os.Looper.loop(Looper.java:130)
06-07 19:55:48.859: E/AndroidRuntime(20274): at android.app.ActivityThread.main(ActivityThread.java:3687)
06-07 19:55:48.859: E/AndroidRuntime(20274): at java.lang.reflect.Method.invokeNative(Native Method)
06-07 19:55:48.859: E/AndroidRuntime(20274): at java.lang.reflect.Method.invoke(Method.java:507)
06-07 19:55:48.859: E/AndroidRuntime(20274): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
06-07 19:55:48.859: E/AndroidRuntime(20274): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
06-07 19:55:48.859: E/AndroidRuntime(20274): at dalvik.system.NativeStart.main(Native Method)
空指针exeception位于lin 118 prepareVideoRecorder（）：
// Step 1: Unlock and set camera to MediaRecorder
mCamera.unlock();
当应用程序启动时，显示摄像头，当我按下按钮时＃34;捕获＆＃34;抛出此错误。现在我认为问题＆＃34; mCamera = getCameraInstance（）;＆＃34;在此函数中再次调用，第一个是在相机预览类的主活动中创建的。
我在＆＃34; mCamera = getCameraInstance（）;＆＃34;之后添加了一个logtag。在prepareVideoRecorder（）中查看它是否真的为空，但是当你看到报告说＆＃34; 06-07 19：55：48.859：D /（20274）：mcamera对象：1＆＃34;
答案 0 :(得分：2)
解决方法是删除行mCamera = getCameraInstance（）;在prepareVideoRecorder（）函数中。
答案 1 :(得分：0)
mMediaRecorder is null，您应该正确初始化它
请查看here。