Tizen Developers

(with internet privilege added in tizen-manifest.xml)

How did  you bring that code up to the shared project ?  Isuppose you are using Xamarin.Forms , right ? 

Yes, I'm using Xamarin.Forms. This code is Tizen specific, it can't be in your Xamarin.Forms shared project. For example, you can add an interface in your Xamarin.Forms shared project :
public interface IPlayer
{
    Task Start(string uri);
 }

In your Tizen projects (in a Tizen class library for example), add the following class :
public class MyPlayer : IPlayer
{
        public async Task Start(string uri)
        {
            var source = new MediaUriSource(uri);
            var player = new Player();
            player.Display = new Display(Forms.Context.MainWindow);
            player.SetSource(source);
            await player.PrepareAsync();
            player.Start();
        }
}

So, you can pass this IPlayer implementation to your App class and you will be able to play a video in your app  :
LoadApplication(new App(new MyPlayer()));