Windows Media Encoder 9 Series enables content owners to protect digital media content during the content creation process. In other words, when you use Windows Media Encoder to encode
content from a source, you can protect the content at the same time, thus eliminating the extra step. As a result, content is never in an unprotected state before you deliver it.
Content that has been encrypted with digital rights management (DRM) technology is called protected content. In order to play back protected content, a user must have the corresponding
license. This separate license "unlocks" the content and determines how the content can be used. For example, a license for promotional content might allow a user to play the
content five times, or the license for rental content might expire after three days.
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Abstract
Microsoft® Windows Media® 9 Series provides support for real-time digital rights management (DRM) protection during the encoding process. This article provides an overview
of the DRM process and describes how to protect content by using Windows Media Encoder.
The license is issued by a third-party license provider. Before you can protect your content, you must set up an account with a license provider and establish the business model and
terms of the licenses for the content.
The following topics introduce you to the DRM process and explain how you can use Windows Media Encoder and DRM to protect content:
Simply put, digital rights management (DRM) is the process of protecting digital media content and controlling its use through rights. Protected content is encrypted with a key, which
is a piece of data that locks and unlocks the content. After the content has been encrypted, a user can only play back the protected file or stream with a separate license. This license
contains the key that decrypts the content and the rights that specify how the content can be used. Users cannot share or copy licenses; however, users can copy and share protected
digital media files with others because the only way to play the protected content is by acquiring a license from the license provider. Therefore, copying protected files does not
compromise their security.
Licenses can grant different combinations of rights depending on the scenario to determine how content can be used. Because the rights are specified in the license, not in the content,
different licenses with different rights can be issued for the same content. Furthermore, because the license is separate from the content, the user needs to acquire the content only
once. For example, a user downloads a song from a Web site and receives a free promotional license allowing her to play the content five times. After she has played the content five
times (and the license has expired), the user can purchase a license that allows an unlimited number of plays for the song she already downloaded.
The following scenario illustrates a typical DRM process. A content owner encodes a song into a Windows Media file and protects it using DRM. The content owner posts the protected
Windows Media file to a Web site, and the file is downloaded by a user. The user's player detects that the file is protected and connects to the license provider's Web site to acquire
the necessary license. The user is notified of the cost of the license. After the user provides payment information, the license provider issues the license, and the user plays the
song. The user then sends the Windows Media file to a friend in an e-mail message. The friend must purchase his own license before he can play the song.
Figure 1 shows the basic DRM process.
Figure 1. The process of using DRM to protect content
The DRM process consists of three steps, which are described in detail in the following sections:
Protecting and distributing content
Playing protected content
Issuing licenses for protected content
Protecting and Distributing Content
Windows Media Encoder 9 Series includes DRM technology that enables you to protect content during the encoding process. To use Windows Media Encoder to protect content, you must first
set up an account with a license provider. The license provider then creates a DRM profile for you, which contains the information required to generate encryption keys. Your license
provider has this same information in order to recreate the encryption keys and include them in the licenses.
Once the account is set up, you can use the DRM profile to protect your content. During the encoding process, the DRM profile adds certain information to the content header (which
is described later in this article), and the content is encrypted. Then, you can distribute your protected content as usual. For example, you can broadcast protected streams, post
protected files on a Web site, or distribute protected content on CDs.
Playing Protected Content
In order to play protected content, users must use a player that supports the Microsoft DRM technology, such as Windows Media Player. (For more information about the latest supported
player, see the Windows Media Web page.) When the user tries to play a protected file or stream, the player searches the user's computer
for a valid license. If the player does not find a valid license, it searches the content header to find the Web address from which a license can be acquired.
The license acquisition process depends on a number of factors, such as whether the user must pay or register for the license. For example, you might distribute promotional content
and have the license provider issue free licenses that expire after a week; since nothing is required in exchange for the license, the license could be issued "silently" without
involving the user. Or, you might require registration information (such as an e-mail address) in exchange for the license. In this case, the user is prompted to fill out a form before
the license is issued.
Once a license has been issued, the user can play the content according to the terms of the license. When the user tries to play content that has an invalid license (for example, a
license that has expired), the license acquisition process begins again.
When you set up an account with a license provider, you and the license provider determine the license acquisition process and the rights that are included in the license.
Issuing Licenses for Protected Content
When a user tries to play protected content for which there is no valid license, the player sends a license request to the license provider. This license request contains the header
of the protected content and the user's system information. The content header includes information such as the Web address from which licenses can be acquired and information about
the content. The system information identifies the user's operating system and player. Because certain operating systems and players have additional security features, the license
provider might issue a less restrictive license based on the system information.
Using the license request, the license provider can determine who owns the content. After identifying the content owner, the license provider can determine which rights to include
in the license and which key to generate. After the user has met the requirements for the license, the license provider issues the license.
Before you can protect your digital media content, you need to set up an account with a license provider. You can contact the license providers directly to find out more information about the DRM services they offer.
After choosing a license provider, you need to set up an account and create a DRM profile. The exact process depends on the license provider, but in general, you will be prompted to
provide personal information for the service (such as your contact and payment information), and your preferences for your licenses (such as the rights to include and the conditions
for issuing licenses). The DRM profile might be created directly on your encoding computer, or it might be created on the license provider's licensing server and then sent to you so
that you can import it to your encoding computer. For information about importing and exporting DRM profiles, see Windows Media Encoder Help.
After you set up an account with a license provider and have a DRM profile, you can begin protecting content, regardless of whether you are distributing content as a file, a stream,
or both. When configuring an encoding session, select the DRM profile on the Security tab of the Session Properties panel. After you finish configuring the encoding session,
apply the settings you specified, and start encoding.
During the content protection process, Windows Media Encoder creates the key to encrypt the content, encrypts the content, and adds DRM-specific information to the content header.
At this time, a key ID is also generated and displayed on the Security tab. The key ID is used in the encryption algorithm, along with other secret values, to generate the encryption
key. The key ID itself is not a secured value; it is stored in the content header. The license provider extracts the key ID value to generate the key to include in the license. Although
you can specify a key ID yourself, it is recommended you let Windows Media Encoder generate a unique value each time you encode, unless you are otherwise instructed by your license
provider.
The figure below shows the Security tab of the Session Properties panel after you apply the configuration settings for the encoding session.
<Figure 2. The Security tab of the Session Properties panel
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