When “media” is discussed in the context of XNA Game Studio, it means
video, songs, or enumeration of items in your media library, including
pictures, album art, songs, and so on.
Although the media APIs exist
on every platform, they were originally designed and intended to be used
on small devices. The first implementation of these APIs was in Game
Studio 3.0 for the Zune device, and the full set of features are now
available on Windows Phone 7, while support for these features is more
limited on Xbox 360 and Windows.
Playing a Song
Playing a song is just as
easy as playing other sound effects, although it does have some special
characteristics. Songs are considered music, and on some platforms can
be overridden by the user. For example, on Xbox 360, if a user picks a
playlist and plays it via the guide in your game, regardless of what
music the game plays, the music the user chooses in the guide is what he
see how easy it is to play a song, create a new game project and add
the samplemusic.mp3 file to your content project. Then, declare a new Song variable to your game:
In your LoadContent method, load the song:
song = Content.Load<Song>("samplemusic");
You’re now ready to play the song. Notice that the song object doesn’t have a Play
method on it like you have seen on the sound effect classes. This is
because there can be only one song playing, where you can have multiple
sound effects playing simultaneously. To play the music directly after
it is created in your LoadContent method, add the following:
Use the MediaPlayer class to control the music. Strictly speaking, the Stop call isn’t required, but just in case something else plays in this sample code, it is inserted directly before the Play method. Before you look at all the information and data you can get from the Song objects, let’s take a quick look at the MediaPlayer class.
There are a few properties on the class you can use to see the current state of what is playing and how. The first one GameHasControl
returns true if the songs you play in your game are actually played,
and false if the system is currently controlling the playback of music
(because the player has requested it as in the previous example). You
don’t have to do anything in response to this, and don’t even need to
check; the system does the right thing, but if you needed to know, you
have that data available.
You can also detect whether the system plays audio via the IsMuted property. Setting this property to true mutes audio currently playing, and setting it to false unmutes it. The IsShuffled
property has an effect only if you’re playing a song list rather than a
single song. When this property is true and it is time to go to the
next song in the list, it randomly picks the next song from the full
list of available songs in the collection rather than simply going to
the next one in the list.
Use the IsRepeating
property to detect or set whether or not the player should repeat
playing from the beginning after it has finished playing its current set
of music. If this is true and you play more than one song, it starts
repeating only after every song in the collection has played.
If the IsVisualizationEnabled property returns true, calls to GetVisualizationData
return data about the currently playing song. Visualization data can be
retrieved during each frame and return a collection of frequencies and a
collection of samples. A common usage of this data is to write
visualizers, which are common in media players that have fancy graphics
seemingly moving with the music.
IsVisualizationEnabled always returns false on Windows Phone 7.
You can use the PlayPosition property to see how far into a given piece of music you are. It returns a TimeSpan of the duration you heard of the song so far. To find the total length of a song, use the Duration property of the song itself.
The Queue property is the current set of songs that is played by the player. It returns a MediaQueue object, which has three pertinent pieces of information on it: the currently active song returned from the ActiveSong property; the index of this song returned from the ActiveSongIndex property; and the total number of songs in this list, naturally returned in the Count property.
You can also get the State of the currently playing media, which returns a MediaState enumeration. The only values of this enumeration (and the only states available) are Playing, Paused, and Stopped.
The last property on the MediaPlayer is Volume,
which is the volume of the music, relative to the current system volume
for music. Volume is defined by decibels, where a value of 0.0f
subtracts 96 decibels from the current volume, and a value of 1.0f does
not modify the volume.
You’ve already seen the Play and Stop method, which are pretty self-explanatory. There are also Pause and Resume methods. Pause and Stop are remarkably similar, in that each of these methods stop the music. Stop, however, resets the current position of the music to the start, and Pause keeps the current position at the moment Pause happened. Resume restarts the music from the current position.
As mentioned, you can have more than one song in a queue. There are two methods to control which song you’re playing, namely MoveNext and MovePrevious. Depending on the state of the IsShuffled property, these methods move to the next or previous song in your list, where the concept of “next” and “previous” are random.
There are also two events you can hook to be notified of status changes of the media played. You can hook the ActiveSongChanged event to see when the current song has changed. This can be from the MoveNext or MovePrevious methods or by the current song ending, and the system automatically moves to a new song.
You can also use the MediaStateChanged event to be notified when the state has changed. As mentioned, these state changes are pause, play, and stop.
Songs and Metadata
At a high level, it is a description of a
song, along with audio data necessary for the media player to play it.
Most of the data is somewhat circular in nature because there are
multiple ways to get to the same data.
The most direct properties for your song are the Name and Duration of the song. You can also get the TrackNumber and PlayCount if these properties exist (they are zero, otherwise). If the IsRated property is true, the Rating property includes the current rating of the song. You can also see whether the song is DRM (Digital Rights Management) protected by looking at the IsProtected property.
You can find out more information about the Artist of the song via the property of the same name, including the Name of the artist, a collection of Songs that the artist has created (including the one you got the artist object from), and a list of Albums the artist has created.
Of course, you can get the Album the song is on, and naturally that object has plenty of information, including the same Artist
you got from the original song object (as mentioned, the references
here can get quite circular). You can also get the collection of Songs that are on the album and the Name and Duration of the album. You can check whether the album has cover art by looking at the HasArt property. If this returns true, you can get the image from the GetAlbumArt method, which returns a Stream that you can use in the Texture2D.FromStream method to create a texture. You can also use the GetThumbnail method to get the art as a thumbnail.
Both the song and the album have a Genre property, which like the album and artist properties also includes a Songs property that is the collection of songs that belong to this genre. It also includes the collection of Albums that belong to the genre, and the Name of the genre itself.
For any given song, you
can reference it four different ways: namely the song itself, through
the album, through the artist, or through the genre. You can also get
any piece of metadata that exists about the song from any of the types.
Use the Song.FromUri to create a Song object from a Web address. This functionality doesn’t work on Xbox 360 and always throws a NotSupportedException.