问Android FOCUS_MODE_CONTINUOUS_VIDEO和捕获预览帧

EN

public void surfaceCreated(SurfaceHolder holder) {
    mCamera = Camera.open();
    try {
        Camera.Parameters parameters = mCamera.getParameters();
        mCamera.setDisplayOrientation(90); // just get it right for testing
        mCamera.setParameters(parameters);
        mCamera.setPreviewDisplay(holder);
        mCamera.setPreviewCallback(new PreviewCallback() {
            public void onPreviewFrame(byte[] data, Camera arg1) {
                Log.d(TAG, String.format("Frame %d", mFrameNumber++)); // see the frames in the logcat
            }
        });
    } catch (IOException exception) {
        mCamera.release();
        mCamera = null;
        Log.d(TAG, "exception setting parameters");
    }
}

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();
    List<Size> previewSizes = parameters.getSupportedPreviewSizes();
    Size previewSize = getOptimalPreviewSize(previewSizes, w, h);
    parameters.setPreviewSize(previewSize.width, previewSize.height);
    parameters.setFocusMode(Parameters.FOCUS_MODE_CONTINUOUS_VIDEO); 
    mCamera.setParameters(parameters);
    mCamera.startPreview();
    if (mRecordingVideo)
        startVideo(mCamera, holder);
}

// derived from http://developer.android.com/guide/topics/media/camera.html#capture-video
private void startVideo(Camera camera, SurfaceHolder holder) {
    camera.stopPreview(); // not specified in documentation but seems to be needed
    camera.unlock();
    mMediaRecorder = new MediaRecorder();
    mMediaRecorder.setCamera(camera);
    mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA); // No audio is recorded
    mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
    mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.MPEG_4_SP);
    mMediaRecorder.setOutputFile("/dev/null");
    try {
        mMediaRecorder.setPreviewDisplay(holder.getSurface());
        mMediaRecorder.prepare();
    } catch (IOException e) {
        camera.release();
        Log.d(TAG, "startVideo: Failed.");
        e.printStackTrace();
    }
    mMediaRecorder.start();
}