media player in webview

im making an android app for an existing website using webview... and i have a problem with the media player... it runs fine but when u click fullscreen it kinda focuses in certain area in the video and does not shrink the video to the right size .. but when i flip the phone to landscape mode everything is fine... so i need help to make the app flip to landscape mode when i click on full screen and retus to portrait mode when i exit fullscreen mode (i waa keep the app in portrait mode all time except when clicking full screen on the video)...here is my app so far:

MainActivity:

public class MainActivity extends Activity {
       WebView myWebView;
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
           myWebView = (WebView) findViewById(R.id.webView1);
           WebSettings webSettings = myWebView.getSettings();
           webSettings.setLoadWithOverviewMode(true);
           webSettings.setUseWideViewPort(true);
           webSettings.setJavaScriptEnabled(true);
           myWebView.setWebViewClient(new WebViewClient() {

                  @Override
                  public void onPageFinished(WebView view, String url) {//this is for handling the white screen that appears while loading
                  super.onPageFinished(view, url);
                  //show webview
                  findViewById(R.id.webView1).setVisibility(View.VISIBLE);
                  //hide loading image
                  findViewById(R.id.pv1).setVisibility(View.INVISIBLE);

                   }
           });
           myWebView.loadUrl("************");

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="e.a.nasrat.hela.MainActivity">
    <WebView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/webView1"
    android:visibility="gone"/>
    <ImageView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/pv1"
    android:visibility="visible"
    android:src="@mipmap/splash"  />
</RelativeLayout>

manifest.xml

   <?xml version="1.0" encoding="utf-8"?>
   <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="e.a.nasrat.hela">
   <uses-permission android:name="android.permission.INTERNET"/>
   <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"   />
   <application
    android:allowBackup="true"
    android:icon="@mipmap/logo"
    android:label="HELA"
    android:supportsRtl="true"
    android:theme="@android:style/Theme.NoTitleBar"
    android:name="Hela"
    android:screenOrientation="portrait">
    <activity android:name=".MainActivity">

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>



   </application>

  </manifest>