Ошибка при инициализации делегата - C#

namespace Chapter_Delegate
{
    public class Media
    {
        public delegate int PlayerD();
        public void Report(PlayerD Play)
        {
            if (Play() == 0) Console.WriteLine("File is played sucsefully.");
            else Console.WriteLine("File is invalid.");
        }
    }
    public class AudioFile
    {
        private int status;
        public int AudioPlay()
        {
            Console.WriteLine("Playing audio file...");
            status = 0;
            return status;
        }
    }
    public class VideoFile
    {
        private int status;
        public int VideoPlay()
        {
            Console.WriteLine("Error by playing, video file is invalid...");
            status = -1;
            return status;
        }
    }
    public class Tester
    {
        public void Run()
        {
            Media myMedia = new Media();
            AudioFile myAu = new AudioFile();
            VideoFile myVd = new VideoFile();
            //instantiate the delegates
            Media.PlayerD MyDA = new Media.PlayerD(myAu.AudioPlay); //- если сделать вне метода Run()  выдает ошибку..
            Media.PlayerD MyDV = new Media.PlayerD(myVd.VideoPlay);// почему компилятор ссылается на Tester.myAu?
        //public void Run() - вне метода не работает, почему?
        //{
            //call the delegates
            myMedia.Report(MyDA);
            myMedia.Report(MyDV);
        }
 
    }
    class Program
    {
        static void Main(string[] args)
        {
            Tester test = new Tester();
            test.Run();
        }
    }
}