Android video recording app nuiances

I have just started Android development.And my goal is to create an android webcam app.

I have taken the base code from here:API Demos and my modified code is included below..

recording happens on click event.But the first time i click, logcat shows me could not connect to camera..

09-25 01:29:58.开发者_如何学Python580: WARN/CameraService(27788): CameraService::connect X (pid 27788) rejected (existing client).
09-25 01:29:58.580: ERROR/StagefrightRecorder(27788): Camera connection could not be established.
09-25 01:29:58.580: WARN/AACEncoder(27788): Call stop() when encoder has not started
09-25 01:29:58.580: WARN/AACEncoder(27788): [ 09-25 01:29:58.580 27788:0x6cd9 F/MPEG4Writer ]
09-25 01:29:58.580: WARN/AACEncoder(27788): frameworks/base/media/libstagefright/MPEG4Writer.cpp:2263 mCodecSpecificData
09-25 01:30:01.130: WARN/IMediaDeathNotifier(28022): media server died
09-25 01:30:01.130: WARN/AudioSystem(1351): AudioFlinger server died!
09-25 01:30:01.140: WARN/Camera(28022): ICamera died
09-25 01:30:01.140: WARN/AudioSystem(1351): AudioPolicyService server died!
09-25 01:30:01.140: WARN/Camera(28022): Camera server died!
09-25 01:30:01.150: ERROR/Camera(28022): Error 100
09-25 01:30:02.639: ERROR/AudioService(1351): Media server started.
09-25 01:30:02.639: ERROR/AudioService(1351): Media server died.
09-25 01:30:02.649: WARN/AudioPolicyManagerBase(28039): setPhoneState() setting same state 0

The second click starts the recording, but on the third click when the recording stops,the screen goes black..though the fourth click does start recording again..

So i have no idea about two things..

1. why the camera fails to connect on first click?
2. why does the screen go black after stopping the recording?

My Modified Code:

public class blueCam extends Activity implements OnClickListener {
    private Preview mPreview;
    Camera mCamera;
    int numberOfCameras;
    int cameraCurrentlyLocked;
    MediaRecorder recorder;
    boolean recording = false;
    // The first rear facing camera
    int defaultCameraId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Hide the window title.
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

        // Create a RelativeLayout container that will hold a SurfaceView,
        // and set it as the content of our activity.
        mPreview = new Preview(this);
        setContentView(mPreview);

        // Find the total number of cameras available
        numberOfCameras = Camera.getNumberOfCameras();

        // Find the ID of the default camera
        CameraInfo cameraInfo = new CameraInfo();
            for (int i = 0; i < numberOfCameras; i++) {
                Camera.getCameraInfo(i, cameraInfo);
                if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
                    defaultCameraId = i;
                }
            }
            mPreview.mSurfaceView.setClickable(true);
            mPreview.mSurfaceView.setOnClickListener(this);
            initRecording();
            
    }

    @Override
    protected void onResume() {
        super.onResume();

        // Open the default i.e. the first rear facing camera.
        mCamera = Camera.open();
        cameraCurrentlyLocked = defaultCameraId;
        mPreview.setCamera(mCamera);
    }

    @Override
    protected void onPause() {
        super.onPause();

        // Because the Camera object is a shared resource, it's very
        // important to release it when the activity is paused.
        if (mCamera != null) {
            mPreview.setCamera(null);
            mCamera.release();
            mCamera = null;
        }
    }
    public void onClick(View v) {
        if (recording) {
            recorder.stop();
            recorder.reset();
            recording = false;

            // Let's initRecorder so we can record again
            
        } else {
            initRecording();
            prepareRecorder();
            recording = true;
            recorder.start();
        }
    }
    public void prepareRecorder() {
        recorder.setPreviewDisplay(mPreview.mHolder.getSurface());

        try {
            recorder.prepare();
        } catch (IllegalStateException e) {
            e.printStackTrace();
            finish();
        } catch (IOException e) {
            e.printStackTrace();
            finish();
        }
    }
    

    public void initRecording()
    {
        String PATH_NAME="/mnt/sdcard/AshVrec.mp4";
        recorder = new MediaRecorder();
        recorder.setVideoSource(MediaRecorder.VideoSource.DEFAULT);
        recorder.setAudioSource(MediaRecorder.AudioSource.DEFAULT);
        CamcorderProfile cpHigh = CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH);
        recorder.setProfile(cpHigh);
        recorder.setOutputFile(PATH_NAME);
        recorder.setMaxDuration(50000); // 50 seconds
        recorder.setMaxFileSize(5000000); // Approximately 5 megabytes

        
        
    }


class Preview extends ViewGroup implements SurfaceHolder.Callback {
    private final String TAG = "Preview";

    SurfaceView mSurfaceView;
    SurfaceHolder mHolder;
    Size mPreviewSize;
    List<Size> mSupportedPreviewSizes;
    Camera mCamera;
    
    Preview(Context context) {
        super(context);
        
        //initRecording();
        mSurfaceView = new SurfaceView(context);
        addView(mSurfaceView);

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = mSurfaceView.getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        
    }
    
   
    public void setCamera(Camera camera) {
        mCamera = camera;
        if (mCamera != null) {
            mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
            requestLayout();
        }
    }

    public void switchCamera(Camera camera) {
       setCamera(camera);
       try {
           camera.setPreviewDisplay(mHolder);
       } catch (IOException exception) {
           Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
       }
       Camera.Parameters parameters = camera.getParameters();
       parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
       requestLayout();

       camera.setParameters(parameters);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // We purposely disregard child measurements because act as a
        // wrapper to a SurfaceView that centers the camera preview instead
        // of stretching it.
        final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        setMeasuredDimension(width, height);

        if (mSupportedPreviewSizes != null) {
            mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, width, height);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if (changed && getChildCount() > 0) {
            final View child = getChildAt(0);

            final int width = r - l;
            final int height = b - t;

            int previewWidth = width;
            int previewHeight = height;
            if (mPreviewSize != null) {
                previewWidth = mPreviewSize.width;
                previewHeight = mPreviewSize.height;
            }

            // Center the child SurfaceView within the parent.
            if (width * previewHeight > height * previewWidth) {
                final int scaledChildWidth = previewWidth * height / previewHeight;
                child.layout((width - scaledChildWidth) / 2, 0,
                        (width + scaledChildWidth) / 2, height);
            } else {
                final int scaledChildHeight = previewHeight * width / previewWidth;
                child.layout(0, (height - scaledChildHeight) / 2,
                        width, (height + scaledChildHeight) / 2);
            }
        }
    }

    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, acquire the camera and tell it where
        // to draw.
        try {
            if (mCamera != null) {
                mCamera.setPreviewDisplay(holder);
            }
        } catch (IOException exception) {
            Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
        }
        //prepareRecorder();
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // Surface will be destroyed when we return, so stop the preview.
        if (mCamera != null) {
            mCamera.stopPreview();
        }
        recorder.stop();
        recorder.reset();
        recorder.release();
    }


    private Size getOptimalPreviewSize(List<Size> sizes, int w, int h) {
        final double ASPECT_TOLERANCE = 0.1;
        double targetRatio = (double) w / h;
        if (sizes == null) return null;

        Size optimalSize = null;
        double minDiff = Double.MAX_VALUE;

        int targetHeight = h;

        // Try to find an size match aspect ratio and size
        for (Size size : sizes) {
            double ratio = (double) size.width / size.height;
            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;
            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }

        // Cannot find the one match the aspect ratio, ignore the requirement
        if (optimalSize == null) {
            minDiff = Double.MAX_VALUE;
            for (Size size : sizes) {
                if (Math.abs(size.height - targetHeight) < minDiff) {
                    optimalSize = size;
                    minDiff = Math.abs(size.height - targetHeight);
                }
            }
        }
        return optimalSize;
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // Now that the size is known, set up the camera parameters and begin
        // the preview.
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
        requestLayout();

        mCamera.setParameters(parameters);
        mCamera.startPreview();
    }

}
}

Any help would be worth. Thanks.