LicenseAcquirer Class

This class knows where to find the PlayReady License Server and how to request a license from that server. This class can be subclassed and overridden to provide custom license-acquiring behavior, such as adding business data or authentication tokens to the request.

Note:
If you start multiple asynchronous operations on the same LicenseAcquirer or DomainAcquirer, an InvalidOperationException is thrown.

You can use a LicenseAcquirer instance in one of the following two states:

1. Attached to a MediaElement.

2. Through AcquireLicenseAsync methods calls.

If you use a LicenseAcquirer instance in state 1, then for the rest of its lifetime, you can only use it through that MediaElement. You cannot reassign the LicenseAcquirer instance to another MediaElement and you cannot use it with the AcquireLicenseAsync methods.

If you use a LicenseAcquirer instance through AcquireLicenseAsync methods calls, then it cannot be assigned to a MediaElement even after the AcquireLicenseAsync operation has fully completed.

When you create a LicenseAcquirer instance, it is in neither state 1 nor state 2. State 1 is only entered when the LicenseAcquirer instance is actually assigned to the MediaElement. State 2 is entered when AcquireLicenseAsync is first called (regardless of success or failure of the operation).

The LicenseAcquirer class is used by the MediaElement to handle acquiring licenses for DRM encrypted content from a PlayReady License Server. You can create a derived class from the LicenseAcquirer class and add custom logic like adding your own custom authentication scheme to the license request.

The following example shows how to override the LicenseAcquirer class (named "ManualLicenseAcquirer") and have a MediaElement use it to acquire the license.

<StackPanel x:Name="LayoutRoot" Background="Gray" Orientation="Vertical">
   <MediaElement x:Name="myME" Height="100"/>
</StackPanel>

In offline scenarios, users download a content file before they play it. Because downloading a media file can take time and bandwidth, consider validating the user license before allowing the download, instead of validating when the user attempts playback. The following example shows how to do this.

The following application uses a key identifier and an authentication token to send a license acquisition request to the license server. The license server responds with a license and the URL from which to download the content.

// Called when the user is online and wants to download some protected content.
public void GetLicensePreDelivery(string customData,
                                     Guid keyId)
{
    Uri licenseServerUrl = new Uri("http://contoso.com/myLicenseServer.asmx");
    LicenseAcquirer acquirer = new LicenseAcquirer();
    acquirer.ChallengeCustomData = customData;

    // Set the License URI to proper License Server address.
    acquirer.LicenseServerUriOverride = licenseServerUrl;
    acquirer.AcquireLicenseCompleted += new EventHandler<AcquireLicenseCompletedEventArgs>(acquirer_Completed);
    acquirer.AcquireLicenseAsync(keyId, ContentKeyType.Aes128Bit, Guid.Empty);
}

The AcquireLicenseAsync call completes after starting the license acquisition but without waiting for the long content download operation to finish. When the license acquisition actually completes, the delegate that is configured on the AcquireLicenseCompleted event is called. In this example, that is the acquirer_Completed method, and it might look something like in the following example.

public void acquirer_Completed(object sender, AcquireLicenseCompletedEventArgs e)
{
    if (e.Error != null)
    {
        // take appropriate action.  Might be retrying for instance.
    }
    else if (e.Cancelled)
    {
        // take appropriate action.  Might be nothing.
    }
    else
    {
        //
        //  We acquired the license successfully, go ahead and download
        //  the content.  Note the service decided to stash the content 
        //  url in the LicenseAcquirer response custom data.
        //
        string contentAcquisitionUrl = e.ResponseCustomData;
        DownloadContent(contentAcquisitionUrl);
    

Windows Phone OS

Windows Phone

Reference

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