To open an embedded video, you need to implement the listener PDFLayoutListener and in the method OnPDFOpenMovie, you can either open the system intent or a custom one...

To open a video using the system intent:

public void OnPDFOpenMovie(String path) {
   Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(path));
   startActivity(intent);
}

To open a video using a custom intent:

public void OnPDFOpenMovie(String path) {
   Intent intent = new Intent(this, VideoPlayer.class);
   intent.putExtra("VIDEOPATH", mVideoPath);
   startActivity(intent);
}

VideoPlayer:

public class VideoPlayer extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_video_player);

VideoView video_player_view = (VideoView) findViewById(R.id.video_player_view);
        video_player_view .setMediaController(new MediaController(this));
        video_player_view .setVideoPath(getIntent().getStringExtra("VIDEOPATH"));
        video_player_view .start();
    }
}

activity_video_player.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen">
    
        <VideoView
            android:id="@+id/video_player_view"
            android:layout_centerInParent="true"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>
    
</RelativeLayout>