Here's the example that's in all the documentation:
Player = Server.Players[0];
// Retrieve the IWMSPlaylist object for the player.
// NOTE: A valid playlist file is not always returned.
// This may be the case, for example, if the user requested
// a specific content file or if a broadcast publishing point
// is being used.
Playlist = Player.RequestedPlaylist;
if (Playlist != null)
{
// Retrieve the IWMSActiveMedia object.
ActiveMedia = Playlist.CurrentMediaInformation;
// Retrieve the IWMSActiveStreams object.
ActiveStreams = ActiveMedia.Streams;