OpenCV, Android, Android-Studio: Detecting Object from video URI

Question

I'm pretty new to android app development, and I'm currently working on a school project that requires my application to capture a video using my android phone and then detect an object in this case the object is a AA battery, using openCV, in the captured video. I'd like to know how I can have OpenCV detect an object in a pre-captured video using the video's uri, I am only capable of detecting an object using openCV's javaCameraView, which is in real-time.

If its not possible for OpenCV to do detection using only the video's URI are there other possible methods? Please note i must use openCV as this is a school project

Here's my java code for the video capturing:

public class MainActivity extends AppCompatActivity {

private Button mRecordView, mPlayView;
private VideoView mVideoView;
private Intent callVideoAppIntent;
private int ACTIVITY_START_CAMERA_APP = 0;
public Uri videoUri;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mRecordView = (Button) findViewById(R.id.btnRecord);
    mPlayView = (Button) findViewById(R.id.btnPlay);
    mVideoView = (VideoView) findViewById(R.id.videoview);


    //Record Button OnClickListener
    mRecordView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            callVideoAppIntent = new Intent();
            callVideoAppIntent.setAction(MediaStore.ACTION_VIDEO_CAPTURE);
            //startActivityForResult(Intent, int RequestCode);
            //application capture video using phone camera,
            //then returns to application after stopping.
            startActivityForResult(callVideoAppIntent, ACTIVITY_START_CAMERA_APP);
        }
    });
    //Play Button OnClickListener
    mPlayView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mVideoView.start();
            mPlayView.setEnabled(false);
            mRecordView.setEnabled(false);
        }
    });

    mVideoView.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
        @Override
        public void onCompletion(MediaPlayer mp) {

            mPlayView.setEnabled(true);
            mRecordView.setEnabled(true);

        }
    });
}
//Once video captured and returned to application,
//we need to capture response,
//on activty result function.
protected void onActivityResult(int requestCode, int resultCode, Intent data){
    if(requestCode == ACTIVITY_START_CAMERA_APP && resultCode == RESULT_OK) {
        videoUri = data.getData();
        mVideoView.setVideoURI(videoUri);
    }
}

}