You need not worry about the file extensions if you use the MediaElement available in the toolbox.
Here's a snippet that can help you:
private void button4_Click(object sender, RoutedEventArgs e)
{
OpenFileDialog ofd = new OpenFileDialog();
ofd.AddExtension = true;
ofd.DefaultExt = "*.*";
ofd.Filter = "Media(*.*)|*.*";
ofd.ShowDialog();
mediaElement1.MediaOpened += new RoutedEventHandler(mediaElement1_MediaOpened);
mediaElement1.Source = new Uri(ofd.FileName);
}
private void button1_Click(object sender, RoutedEventArgs e)
{
mediaElement1.Play();
}
private void button3_Click(object sender, RoutedEventArgs e)
{
mediaElement1.Stop();
}
private void button2_Click(object sender, RoutedEventArgs e)
{
mediaElement1.Pause();
}
For more details refer to: http://bitsandbinaries.wordpress.com/net-programming/wpfwindows-presentation-foundation/a-simple-media-player-program-in-c-net-4-0/