Permanently hide Navigation Bar in an activity

Is it possible to permanently remove the Navigation Bar on an activity? I want to remove the bar with the buttons that appear at the button of the screen on a tablet, not the Action Bar. Here.

I know it is not recommended to do that, I did not make this decision, but I need to do it. On my layout, there is another button to leave the activity. The rest of my app can have and does have the Navigation Bar.

I found this code and adapted it a little bit. The problem is that even when I hide the Navigation Bar, there is a black space left behind. I guess the system calculates the screen size having into account the navigation bar?

public static class Content extends ImageView implements View.OnSystemUiVisibilityChangeListener, View.OnClickListener, ActionBar.OnMenuVisibilityListener {
    Activity mActivity;
    TextView mTitleView;
    Button mPlayButton;
    SeekBar mSeekView;
    boolean mAddedMenuListener;
    boolean mMenusOpen;
    boolean mPaused;
    boolean mNavVisible;
    int mLastSystemUiVis;

    Runnable mNavHider = new Runnable() {
        @Override public void run() {
            setNavVisibility(false);
        }
    };

    public Content(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOnSystemUiVisibilityChangeListener(this);
        setOnClickListener(this);
    }

    public void init(Activity activity, TextView title, Button playButton,
            SeekBar seek) {
        // This called by the containing activity to supply the surrounding
        // state of the video player that it will interact with.
        mActivity = activity;
        mTitleView = title;
        mPlayButton = playButton;
        mSeekView = seek;
        mPlayButton.setOnClickListener(this);
        setPlayPaused(true);
    }

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