SoundEffect and SoundEffectInstance when in Windows Phone Silverlight app - silverlight

Question

Windows Phone 7.1/7.5/Mango Silverlight app.
I used the Sound Sample example here to implement playing sounds in my app.
Here's the snippet.
//The sounds to play
private SoundEffect coyoteSound;
private SoundEffect birdSound;
//Constructor
public MainPage()
{
InitializeComponent();
// Prime the pump or we'll get an exception.
FrameworkDispatcher.Update();
// Create and load SoundEffect objects.
LoadSound("Resources/coyoteSound.wav", out coyoteSound);
LoadSound("Resources/birdSound.wav", out birdSound);
}
/// <summary>
/// Loads a wav file into an XNA Framework SoundEffect.
/// </summary>
/// <param name="SoundFilePath">Relative path to the wav file.</param>
/// <param name="Sound">The SoundEffect to load the audio into.</param>
private void LoadSound(String SoundFilePath, out SoundEffect Sound)
{
// For error checking, assume we'll fail to load the file.
Sound = null;
try
{
// Holds informations about a file stream.
StreamResourceInfo SoundFileInfo = App.GetResourceStream(new Uri(SoundFilePath, UriKind.Relative));
// Create the SoundEffect from the Stream
Sound = SoundEffect.FromStream(SoundFileInfo.Stream);
}
catch (NullReferenceException)
{
// Display an error message
MessageBox.Show("Couldn't load sound " + SoundFilePath);
}
}
//Play sound when page naivgateTo
protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgse)
{
birdSound.Play();
}
//Common mouseclick handler to play sound
private void ElementClick_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
FrameworkElement ele = sender as FrameworkElement;
if (ele != null)
{
switch (ele.Name)
{
case "imgcoyoteSound":
coyoteSound.Play();
break;
case "imgbirdSound":
birdSound.Play();
break;
default:
birdSound.Play();
break;
}
}
}
Questions:
1: I want to Stop the sound and I see I need to use SoundEffectInstance for that. What is the best way to integrate those in my above code.
2: The sound in the OnNavigatedTo starts playing even before my page is loaded? I tried putting the play in OnLoaded but still the say. Any ideas on that?
3: I read about being careful on Memory Usage when using SoundEffect/SoundEffectInstance. Will the above code cause any memory issue?
4:Most of my pages (20-25) will have sound effects implementation like above. That shouldn't be an issue correct?
Update: Is is right place to call dispose? Will it affect the sound play when I go to this page using Back button?
//Play sound when page naivgateFrom
protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgse)
{
birdSoundEffectInstance.Dispose();
coyoteSoundEffectInstance.Dispose();
}

Answer 1

SoundEffectInstances are fairly simple to implement, assuming silverlight works like regular XNA.
SoundEffectInstance birdSoundInstance = birdSound.CreateInstance();
Usage of a SoundEffectInstance is similar to a SoundEffect, except with a lot more control. You can choose stereo panning position, pitch and volume, set the sound to loop, pause the sound, etc. Just keep a reference to the Instance around and use one of its methods for these actions. I would recommend just adding a birdSoundInstance and coyoteSoundInstance alongside your SoundEffects in class properties, I guess.
Memory is not as much of an issue on Windows Phone because the platform limits you to 16 SoundEffectInstances playing at once. So, essentially, it won't let you use large amounts of memory (unless you're playing 16 very large sounds). What I like to do is make a singleton for playing music which has an array of 16 sounds. When I call .PlaySound(SoundEffectInstance sound), it checks for an empty spot in the array to place that sound in. If there is none, it replaces the oldest sound. It checks every frame for stopped (ended) sounds in the array and flushes them out, disposing them. (A Queue might seem like a good data structure to do this, but it is restrictive about removing sounds which have ended).
Another thing to note when using SoundEffectInstances is that they continue to exist even if you dereference them, in my experience. If you want to stop playing an instance you need to either let it finish or command it to stop. Note that SoundEffectInstance has a Dispose() method. Use this when you are done playing the sound to remove it from memory. I don't think the garbage collector automatically picks them up like most other assets.
I'm not sure I can help with your code as it seems Silverlight asset loading is significantly different from XNA pipeline loading, but I hope I've shed some light on the subject. I think sounds are some of the easier things to do in XNA.