Windows.UI.Xaml.Controls.MediaPlayerElement without HttpClient sample:
mediaPlayer = new MediaPlayerElement();
mediaPlayer.AutoPlay = true;
this.Content = mediaPlayer;
Uri uri = new Uri("http://video.ch9.ms/ch9/70cc/83e17e76-8be8-441b-b469-87cf0e6a70cc/ASPNETwithScottHunter_high.mp4");
mediaPlayer.SetMediaPlayer(new Windows.Media.Playback.MediaPlayer());
mediaPlayer.Source = Windows.Media.Core.MediaSource.CreateFromUri(uri);
Easy!