Package | flash.media |
Class | public class SoundLoaderContext |
Inheritance | SoundLoaderContext Object |
Language Version: | ActionScript 3.0 |
Runtime Versions: | AIR 1.0 Flash Player 9 |
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 theSoundMixer.computeSpectrum()
,SoundMixer.bufferTime
, andSoundTransform()
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 following:
- The security chapter in the Programming ActionScript 3.0 book and the latest comments on LiveDocs
- The security chapter in the Programming ActionScript 3.0 book and the latest comments on LiveDocs
- The "Understanding AIR Security" section of the "Getting started with Adobe AIR" chapter in the Developing AIR Applications book.
- The Flash Player Developer Center Topic: Security
Property | Defined By | ||
---|---|---|---|
bufferTime : Number = 1000
The number of milliseconds to preload a streaming sound into a buffer
before the sound starts to stream. | SoundLoaderContext | ||
checkPolicyFile : Boolean = false
Specifies whether the application should try to download a URL policy file from the
loaded sound's server before beginning to load the sound. | SoundLoaderContext | ||
constructor : Object
A reference to the class object or constructor function for a given object instance. | Object | ||
prototype : Object [static]
A reference to the prototype object of a class or function object. | Object |
Method | Defined By | ||
---|---|---|---|
Creates a new sound loader context object. | SoundLoaderContext | ||
Indicates whether an object has a specified property defined. | Object | ||
Indicates whether an instance of the Object class is in the prototype chain of the object specified
as the parameter. | Object | ||
Indicates whether the specified property exists and is enumerable. | Object | ||
Sets the availability of a dynamic property for loop operations. | Object | ||
Returns the string representation of this object, formatted according to locale-specific conventions. | Object | ||
Returns the string representation of the specified object. | Object | ||
Returns the primitive value of the specified object. | Object |
bufferTime | property |
public var bufferTime:Number = 1000
Language Version: | ActionScript 3.0 |
Runtime Versions: | AIR 1.0 Flash Player 9 |
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 | property |
public var checkPolicyFile:Boolean = false
Language Version: | ActionScript 3.0 |
Runtime Versions: | AIR 1.0 Flash Player 9 |
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 asURLRequest.url
. (The sound's URL is specified in theurl
property of the URLRequest object passed toSound.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 on policy files, see the "Flash Player Security" chapter in Programming ActionScript 3.0.
See also
SoundLoaderContext | () | Constructor |
public function SoundLoaderContext(bufferTime:Number = 1000, checkPolicyFile:Boolean = false)
Language Version: | ActionScript 3.0 |
Runtime Versions: | AIR 1.0 Flash Player 9 |
Creates a new sound loader context object.
ParametersbufferTime:Number (default = 1000 ) — The number of seconds to preload a streaming sound into a buffer
before the sound starts to stream.
| |
checkPolicyFile:Boolean (default = false ) — Specifies whether the existence of a URL policy file
should be checked upon loading the object (true ) or not.
|
Example ( How to use this example )
The first parameter of a SoundLoaderContext object (context
) is used to increase
the default buffer value of one second to three seconds. (The value is in milliseconds.)
If the second parameter of the SoundLoaderContext object is set to true
,
Flash Player will check for a cross-domain policy file upon loading the object. Here it is
set to the default value false
, so no policy file will be checked.
The load()
method of the sound object will use the context setting to make sure
it will take three seconds to preload the streaming sound into a buffer before the sound starts
to stream. The URLRequest
object determines the location of the file, which is a
podcast from Adobe. If an IOErrorEvent.IO_ERROR
error occurs during the loading
of the sound file, the errorHandler()
method is invoked.
package { import flash.display.Sprite; import flash.net.URLRequest; import flash.media.Sound; import flash.media.SoundLoaderContext; import flash.events.IOErrorEvent; public class SoundLoaderContextExample extends Sprite { public function SoundLoaderContextExample() { var snd:Sound = new Sound(); var req:URLRequest = new URLRequest("http://av.adobe.com/podcast/csbu_dev_podcast_epi_2.mp3"); var context:SoundLoaderContext = new SoundLoaderContext(3000, false); snd.load(req, context); snd.play(); snd.addEventListener(IOErrorEvent.IO_ERROR, errorHandler); } private function errorHandler(errorEvent:IOErrorEvent):void { trace("The sound could not be loaded: " + errorEvent.text); } } }
Fri Mar 19 2010, 02:45 AM -07:00