Android Camera2 api, Swap cameras quickly on the go

Question

I'm making an Android app using the Camera2 api.

I want to be able to switch between the front and back camera, but it takes an awful lot of time to do so no matter how i try to implement it.

After what i understand, you can't open both cameras at once(i've tried that also), so you have to stop the first one before opening the second.

The problem is it takes me 1.5seconds to stop the first camera.

How does for instance snapchat manage to swap the cameras in a few hundred milliseconds?

---

The code i'm using is the camera2basic from google that can be found here:

https://github.com/googlesamples/android-Camera2Basic/blob/master/Application/src/main/java/com/example/android/camera2basic/Camera2BasicFragment.java

I've added a simple method to stop the camera:

public void stopCamera(){
    Log.i("yoyo","Stopcamera() begin");
    mCameraDevice.close();
    //stopBackgroundThread();
    Log.i("yoyo","Stopcamera() end");
}

Android Monitor:

08-01 15:13:01.478 10020-10020/com.example.android.camera2basic I/yoyo: Stopcamera() begin 08-01 15:13:02.852 10020-10020/com.example.android.camera2basic I/yoyo: Stopcamera() end 08-01 15:13:02.853 10020-10020/com.example.android.camera2basic I/Choreographer: Skipped 81 frames! The application may be doing too much work on its main thread. 08-01 15:13:02.855 10020-10207/com.example.android.camera2basic I/yoyo: Cameradevice - onClosed() callback running

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-UPDATE 07 aug 2017-

It seems that the camera2 api just takes longer to shut down than the old camera api.

I tried using the old camera api and I achieved the same speed as snapchat/instagram, so i'm guessing they are using the old camera api.

Answer 1

You should be able to run both capture sessions concurrently. You can even have both "previews" on the UI at the same time.

Here's what you have to do:

• create device 1 (i.e. back camera) with cameraManager.openCamera("1", ...)
• create device 2 (i.e. front camera) cameraManager.openCamera("2", ...)
• Once you have a CameraDevice instance for each camera, start their capture session
• cameraDevice1.createCaptureSession(surface1, ...)
• cameraDevice1.createCaptureSession(surface2, ...)
• When the capture sessions are created successfully, you should be at to call captureSession.setRepeatingRequest(...).

As you've noticed, there's a huge overhead in switching cameras from "scratch". If you only want to show one preview at a time. You can still call openCamera() for each camera, call createCaptureRequest for each camera, and use setRepeatingRequest or stopRepeating to control when the captureSession is actually processing frames.

Hope this helps!

Answer 2

William Guedes

Here's what you have to do:

create device 1 (i.e. back camera) with cameraManager.openCamera("1", ...)

create device 2 (i.e. front camera) cameraManager.openCamera("2", ...)

I've written some simple code below for opening both cameras using manager.openCamera().

The monitor only logs "camera 0 onOpened() callback" though, and i assumed this ment you could only open one camera at the time?

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.e("yoyo", "onCreate() begin");
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
           
        try {

            String[] cameraIdList = manager.getCameraIdList();

            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE}, 123);
                return;
            }
            manager.openCamera(cameraIdList[0], new CameraDevice.StateCallback() {
                @Override
                public void onOpened(@NonNull CameraDevice cameraDevice) {
                    Log.e("yoyo", "camera 0 onOpened() callback");
                }

                @Override
                public void onDisconnected(@NonNull CameraDevice cameraDevice) {

                }

                @Override
                public void onError(@NonNull CameraDevice cameraDevice, int i) {

                }
            }, null);

            manager.openCamera(cameraIdList[1], new CameraDevice.StateCallback() {
                @Override
                public void onOpened(@NonNull CameraDevice cameraDevice) {
                    Log.e("yoyo", "camera 1 onOpened() callback");
                }

                @Override
                public void onDisconnected(@NonNull CameraDevice cameraDevice) {

                }

                @Override
                public void onError(@NonNull CameraDevice cameraDevice, int i) {

                }
            }, null);


        }catch (CameraAccessException e) {e.printStackTrace();}


    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == 123) {
            if (grantResults[0] == PackageManager.PERMISSION_DENIED) {
                // close the app
                Toast.makeText(this, "Sorry!!!, you can't use this app without granting permission", Toast.LENGTH_LONG).show();
                finish();
            }
        }
    }
}