1. Make sure you've got Android Studio up and running.
2. Start a new Android project or just open one you already have.
3. Head over to the Firebase Console at Firebase Console.
4. Add your Android app to your Firebase project.

• Enter your app's package name.
• Follow the steps to download the google-services.json file.

1. Drop the google-services.json file into the app/ directory of your project.

2. Add this classpath to your project's build.gradle file:
   ```groovy
   buildscript {
   dependencies {
   // Add this line
   classpath 'com.google.gms:google-services:4.3.10'
   }
   }
   ```

3. In the app-level build.gradle file, apply the following plugin and dependencies:
   ```groovy
   apply plugin: 'com.android.application'
   apply plugin: 'com.google.gms.google-services'

   dependencies {
   // Add these lines
   implementation 'com.google.firebase:firebase-ml-vision:24.0.3'
   implementation 'com.google.firebase:firebase-analytics'
   }
   ```

1. Open up AndroidManifest.xml.
2. Add these permissions and features:
   ```xml \`\`\`

1. Create a file called CameraSource.java to handle camera operations.

2. Implement the code to preview camera input:
   ```java
   import android.hardware.Camera;
   import android.view.SurfaceHolder;
   import android.view.SurfaceView;
   import java.io.IOException;

   public class CameraSource extends SurfaceView implements SurfaceHolder.Callback {
   private Camera camera;
   
   public CameraSource(Context context) {
   super(context);
   camera = Camera.open();
   SurfaceHolder holder = getHolder();
   holder.addCallback(this);
   }
   
   @Override
   public void surfaceCreated(SurfaceHolder holder) {
   try {
   camera.setPreviewDisplay(holder);
   camera.startPreview();
   } catch (IOException e) {
   e.printStackTrace();
   }
   }
   
   @Override
   public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
   // Handle surface changes here
   }
   
   @Override
   public void surfaceDestroyed(SurfaceHolder holder) {
   camera.release();
   }
   }
   ```

1. In your main activity, set up Firebase Vision and create a face detector instance:
   ```java
   import com.google.firebase.ml.vision.FirebaseVision;
   import com.google.firebase.ml.vision.common.FirebaseVisionImage;
   import com.google.firebase.ml.vision.face.FirebaseVisionFace;
   import com.google.firebase.ml.vision.face.FirebaseVisionFaceDetector;
   import com.google.firebase.ml.vision.face.FirebaseVisionFaceDetectorOptions;

   import java.util.List;

   public class MainActivity extends AppCompatActivity {
   private CameraSource cameraSource;
   
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(new CameraSource(this));
   
   FirebaseVisionFaceDetectorOptions options =
   new FirebaseVisionFaceDetectorOptions.Builder()
   .setPerformanceMode(FirebaseVisionFaceDetectorOptions.ACCURATE)
   .setLandmarkMode(FirebaseVisionFaceDetectorOptions.ALL_LANDMARKS)
   .setClassificationMode(FirebaseVisionFaceDetectorOptions.ALL_CLASSIFICATIONS)
   .build();
   
   FirebaseVisionFaceDetector detector = FirebaseVision.getInstance()
   .getVisionFaceDetector(options);
   }
   
   private void detectFaces(FirebaseVisionImage image) {
   detector.detectInImage(image)
   .addOnSuccessListener(new OnSuccessListener<List>() {
   @Override
   public void onSuccess(List faces) {
   for (FirebaseVisionFace face : faces) {
   // Handle detected faces here
   }
   }
   })
   .addOnFailureListener(new OnFailureListener() {
   @Override
   public void onFailure(@NonNull Exception e) {
   // Handle detection failure here
   }
   });
   }
   }
   ```

1. Modify the CameraSource class to capture frames and use the face detector:
   ```java
   import android.graphics.Bitmap;
   import android.hardware.Camera;
   import com.google.firebase.ml.vision.common.FirebaseVisionImage;

   public CameraSource(Context context) {
   super(context);
   camera = Camera.open();
   camera.setPreviewCallback(new Camera.PreviewCallback() {
   @Override
   public void onPreviewFrame(byte[] data, Camera camera) {
   Camera.Parameters parameters = camera.getParameters();
   int width = parameters.getPreviewSize().width;
   int height = parameters.getPreviewSize().height;
   Bitmap bitmap = BitmapUtils.getBitmapFromYUV(data, width, height);
   FirebaseVisionImage image = FirebaseVisionImage.fromBitmap(bitmap);
   
   // Call detectFaces method from MainActivity here
   ((MainActivity)context).detectFaces(image);
   }
   });
   SurfaceHolder holder = getHolder();
   holder.addCallback(this);
   }
   ```

2. Create BitmapUtils class to convert YUV data to Bitmap:
   ```java
   import android.graphics.Bitmap;
   import android.graphics.YuvImage;

   public class BitmapUtils {
   public static Bitmap getBitmapFromYUV(byte[] data, int width, int height) {
   YuvImage yuvImage = new YuvImage(data, ImageFormat.NV21, width, height, null);
   ByteArrayOutputStream out = new ByteArrayOutputStream();
   yuvImage.compressToJpeg(new Rect(0, 0, width, height), 50, out);
   byte[] bytes = out.toByteArray();
   return BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
   }
   }
   ```

By following these steps, Firebase ML Kit Face Detection can be effectively integrated into an Android app. Each step ensures proper setup and use of the camera and Firebase Vision API to detect faces in real-time.