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Class SoundLoaderContext

The SoundLoaderContext class provides security checks for files that load sound. SoundLoaderContext objects are passed as an argument to the constructor and the load() method of the Sound class.

When you use this class, consider the following security model:

  • Loading and playing a sound is not allowed if the calling file is in a network sandbox and the sound file to be loaded is local.
  • By default, loading and playing a sound is not allowed if the calling is local and tries to load and play a remote sound. A user must grant explicit permission to allow this.
  • Certain operations dealing with sound are restricted. The data in a loaded sound cannot be accessed by a file in a different domain unless you implement a URL policy file. Sound-related APIs that fall under this restriction are the Sound.id3 property and the SoundMixer.computeSpectrum(), SoundMixer.bufferTime, and SoundTransform() methods.

However, in Adobe AIR, content in the application security sandbox(content installed with the AIR application) are not restricted by these security limitations.

For more information related to security, see the Flash Player Developer Center Topic: Security.

Hierarchy

  • SoundLoaderContext

Index

Constructors

Properties

Constructors

constructor

  • new SoundLoaderContext(bufferTime?: number, checkPolicyFile?: boolean): SoundLoaderContext

  • Creates a new sound loader context object.

    Parameters

    • Optional bufferTime: number

      The number of seconds to preload a streaming sound into a buffer before the sound starts to stream.

    • Optional checkPolicyFile: boolean

      Specifies whether the existence of a URL policy file should be checked upon loading the object (true) or not.

    Returns SoundLoaderContext

Properties

bufferTime

bufferTime: number

The number of milliseconds to preload a streaming sound into a buffer before the sound starts to stream.

Note that you cannot override the value of SoundLoaderContext.bufferTime by setting the global SoundMixer.bufferTime property. The SoundMixer.bufferTime property affects the buffer time for embedded streaming sounds in a SWF file and is independent of dynamically created Sound objects(that is, Sound objects created in ActionScript).

checkPolicyFile

checkPolicyFile: boolean

Specifies whether the application should try to download a URL policy file from the loaded sound's server before beginning to load the sound. This property applies to sound that is loaded from outside the calling file's own domain using the Sound.load() method.

Set this property to true when you load a sound from outside the calling file's own domain and code in the calling file needs low-level access to the sound's data. Examples of low-level access to a sound's data include referencing the Sound.id3 property to get an ID3Info object or calling the SoundMixer.computeSpectrum() method to get sound samples from the loaded sound. If you try to access sound data without setting the checkPolicyFile property to true at loading time, you may get a SecurityError exception because the required policy file has not been downloaded.

If you don't need low-level access to the sound data that you are loading, avoid setting checkPolicyFile to true. Checking for a policy file consumes network bandwidth and might delay the start of your download, so it should only be done when necessary.

When you call Sound.load() with SoundLoaderContext.checkPolicyFile set to true, Flash Player or AIR must either successfully download a relevant URL policy file or determine that no such policy file exists before it begins downloading the specified sound. Flash Player or AIR performs the following actions, in this order, to verify the existence of a policy file:

  • Flash Player or AIR considers policy files that have already been downloaded.
  • Flash Player or AIR tries to download any pending policy files specified in calls to Security.loadPolicyFile().
  • Flash Player or AIR tries to download a policy file from the default location that corresponds to the sound's URL, which is /crossdomain.xml on the same server as URLRequest.url.(The sound's URL is specified in the url property of the URLRequest object passed to Sound.load() or the Sound() constructor function.)

In all cases, Flash Player or AIR requires that an appropriate policy file exist on the sound's server, that it provide access to the sound file at URLRequest.url by virtue of the policy file's location, and that it allow the domain of the calling file to access the sound, through one or more <allow-access-from> tags.

If you set checkPolicyFile to true, Flash Player or AIR waits until the policy file is verified before loading the sound. You should wait to perform any low-level operations on the sound data, such as calling Sound.id3 or SoundMixer.computeSpectrum(), until progress and complete events are dispatched from the Sound object.

If you set checkPolicyFile to true but no appropriate policy file is found, you will not receive an error until you perform an operation that requires a policy file, and then Flash Player or AIR throws a SecurityError exception. After you receive a complete event, you can test whether a relevant policy file was found by getting the value of Sound.id3 within a try block and seeing if a SecurityError is thrown.

Be careful with checkPolicyFile if you are downloading sound from a URL that uses server-side HTTP redirects. Flash Player or AIR tries to retrieve policy files that correspond to the url property of the URLRequest object passed to Sound.load(). If the final sound file comes from a different URL because of HTTP redirects, then the initially downloaded policy files might not be applicable to the sound's final URL, which is the URL that matters in security decisions.

If you find yourself in this situation, here is one possible solution. After you receive a progress or complete event, you can examine the value of the Sound.url property, which contains the sound's final URL. Then call the Security.loadPolicyFile() method with a policy file URL that you calculate based on the sound's final URL. Finally, poll the value of Sound.id3 until no exception is thrown.

This does not apply to content in the AIR application sandbox. Content in the application sandbox always has programatic access to sound content, regardless of its origin.

For more information related to security, see the Flash Player Developer Center Topic: Security.

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