Encrypted Media Extensions

Abstract

This proposal extends HTMLMediaElement providing APIs to control playback of protected content.

The API supports use cases ranging from simple clear key decryption to high value video (given an appropriate user agent implementation). License/key exchange is controlled by the application, facilitating the development of robust playback applications supporting a range of content decryption and protection technologies.

This specification does not define a content protection or Digital Rights Management system. Rather, it defines a common API that may be used to discover, select and interact with such systems as well as with simpler content encryption systems. Implementation of Digital Rights Management is not required for compliance with this specification: only the simple clear key system is required to be implemented as a common baseline.

The common API supports a simple set of content encryption capabilities, leaving application functions such as authentication and authorization to page authors. This is achieved by requiring content protection system-specific messaging to be mediated by the page rather than assuming out-of-band communication between the encryption system and a license or other server.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Implementers should be aware that this specification is not stable. Implementers who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should join the mailing list mentioned below and take part in the discussions.

This document was published by the HTML working group as an Editor's Draft. Please submit comments regarding this document by using the W3C's (public bug database) with the product set to HTML WG and the component set to Encrypted Media Extensions. If you cannot access the bug database, submit comments to public-html-media@w3.org (subscribe, archives) and arrangements will be made to transpose the comments to the bug database. All feedback is welcome.

Publication as an Editor's Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

Note: It is an open issue whether and how the spec should do more to encourage/ensure CDM-level interop. See Bug 20944.

Note: This specification contains sections for describing security and privacy considerations. These sections are not final and review is welcome.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

• 1. Introduction
• • 1.1. Definitions
• 2. Media Element Extensions
• • 2.1. Exceptions
  • 2.2. MediaKeyError
  • 2.3. Media Element Restrictions
• 3. Events
• • 3.1 Event Definitions
  • 3.2 Event Summary
• 4. Algorithms
• • 4.1. Initialization Data Encountered
  • 4.2. Encrypted Block Encountered
  • 4.3. Queue a "message" Event
  • 4.4. Queue an "error" Event
  • 4.5. Usable Keys Changed
  • 4.6. Update Expiration
  • 4.7. Session Close
  • 4.8. Queue a "waiting" Event
  • 4.9. Attempt to Resume Playback If Necessary
• 5. Simple Decryption
• • 5.1. Clear Key
• 6. Security Considerations
• 7. Privacy Considerations
• 8. Examples
• 9. Revision History

1. Introduction

This section is non-normative.

This proposal allows JavaScript to select content protection mechanisms, control license/key exchange, and implement custom license management algorithms. It supports a wide range of use cases without requiring client-side modifications in each user agent for each use case. This also enables content providers to develop a single application solution for all devices. A generic stack implemented using the proposed APIs is shown below. This diagram shows an example flow: other combinations of API calls and events are possible.

1.1. Definitions

Text in this font and color is non-normative.

1.1.1. Content Decryption Module (CDM)

The Content Decryption Module (CDM) is a generic term for the client component that provides the functionality, including decryption, for one or more Key Systems.

Implementations may or may not separate the implementations of CDMs or treat them as separate from the user agent. This is transparent to the API and application. A user agent may support one or more CDMs.

1.1.2. Key System

A Key System is a generic term for a decryption mechanism and/or content protection provider. Key System strings provide unique identification of a Key System. They are used by the user agent to select the Content Decryption Modules and identify the source of a key-related event. Simple Decryption Key Systems are supported by all user agents. User agents may also provide additional CDMs with corresponding Key System strings.

A Key System string is always a reverse domain name. For example, "com.example.somesystem". Key System strings are compared using case-sensitive matching. It is recommended that CDMs use simple lower-case ASCII key system strings.

Within a given system ("somesystem" in the example), subsystems may be defined as determined by the key system provider. For example, "com.example.somesystem.1" and "com.example.somesystem.1_5". Key System providers should keep in mind that these will be used for comparison and discovery, so they should be easy to compare and the structure should remain reasonably simple.

1.1.3. Key Session

A Key Session, or simply Session, provides a context for message exchange with the CDM as a result of which key(s) are made available to be CDM. Sessions are embodied as MediaKeySession objects. Each Key session is associated with a single instance of Initialization Data provided in the createSession() call.

Each Key Session is associated with a single MediaKeys object, and only media elements associated with that object may access key(s) associated with the session. Other MediaKeys objects, CDM instances, and media elements may not access the key session or use its key(s). Key sessions and the keys they contain are no longer usable by the CDM for decryption when the session is closed, including when the MediaKeySession object is destroyed.

1.1.4. Session ID

A Session ID is a unique string identifier generated by the user agent or CDM that can be used by the application to identify MediaKeySession objects. (The underlying content protection client or server do not necessarily need to support Session IDs.)

A new Session ID is generated each time the user agent and CDM successfully create a new session.

Each Session ID shall be unique within the browsing context in which it was created. (Note: Some use cases may require that Session IDs be unique within the origin over time, including across browsing sessions.)

1.1.5. Key

Unless otherwise stated, key refers to a decryption key that can be used to decrypt blocks within media data. Each such key is uniquely identified by a key ID. A key is associated with the session used to provide it to the CDM. (The same key may be present in multiple sessions.) Such keys may only be provided to the CDM via an update() call. (They may later be loaded by loadSession() as part of the stored session data.)

A key is considered usable if the CDM is certain the key is currently usable for decryption. For example, a key is not usable if its license has expired.

1.1.6. Key ID

A key is associated with a key ID, which uniquely identifies a key. The container specifies the ID of the key that can decrypt a block or set of blocks within the media data. Initialization Data may contain key ID(s) to identify the keys that are needed to decrypt the media data. However, there is no requirement that Initialization Data contain any or all key IDs used in the media data or media resource. Licenses provided to the CDM associate each key with a key ID so the CDM can select the appropriate key when decrypting an encrypted block of media data.

1.1.7. License

A license is key system-specific state information that includes one or more key(s) - each associated with a key ID - and potentially other information about key usage.

1.1.8. Initialization Data

Key Systems usually require a block of initialization data containing information about the stream to be decrypted before they can construct a license request message. This block could be a simple key or content ID or a more complex structure containing such information. It should always allow unique identification of the key(s) needed to decrypt the content. This initialization information may be obtained in some application-specific way or provided with the media data.

Initialization Data is a generic term for container-specific data that is used by CDMs to generate a license request. Initialization data found with the media data is provided to the application in the initData attribute of the needkey event.

The format of the initialization data depends upon the type of container, and containers may support more than one format of initialization data. The initialization data type is a string that indicates what format the initialization data is provided in. Initialization data type strings are always matched case-sensitively. It is recommended that initialization data type strings are lower-case ASCII strings.

The Encrypted Media Extensions Stream Format and Initialization Data Format Registry provides the mapping from initialization data type string to the specification for each format.

1.1.9. Cross Origin Support

During playback, embedded media data is exposed to script in the embedding origin. In order for the API to fire needkey and message events, media data must be CORS-same-origin with the embedding page. If media data is cross-origin with the embedding document, authors should use the crossorigin attribute on the media element and CORS headers on the media data response to make it CORS-same-origin.

2. Media Element Extensions

We extend media element to allow decryption key acquisition to be handled by the application.

enum MediaWaitingFor { "none", "data", "key" };
partial interface HTMLMediaElement {
  // Encrypted Media
  readonly attribute MediaKeys? mediaKeys;
  Promise<any> setMediaKeys(MediaKeys? mediaKeys);
  
  attribute EventHandler onneedkey;

  readonly attribute MediaWaitingFor waitingFor;
};

enum IsTypeSupportedResult { "" /* empty string */, "maybe", "probably" };
enum SessionType { "temporary", "persistent" };
interface MediaKeys {
  readonly attribute DOMString keySystem;

  Promise<MediaKeySession> createSession(DOMString initDataType, (ArrayBuffer or ArrayBufferView) initData, optional SessionType sessionType = "temporary");
  Promise<MediaKeySession> loadSession(DOMString sessionId);
  Promise<any> setServerCertificate((ArrayBuffer or ArrayBufferView) serverCertificate);

  static Promise<MediaKeys> create(DOMString keySystem)
  static IsTypeSupportedResult isTypeSupported(DOMstring keySystem, optional DOMString initDataType, optional DOMString contentType, optional DOMString capability);
};

interface MediaKeySession : EventTarget {
  // error state
  readonly attribute MediaKeyError? error;

  // session properties
  readonly attribute DOMString sessionId;
  readonly attribute unrestricted double expiration;
  readonly attribute Promise<any> closed;

  // session operations
  Promise<any> update((ArrayBuffer or ArrayBufferView) response);
  Promise<any> close();
  Promise<any> remove();
  
  Promise<sequence<ArrayBuffer>> getUsableKeyIds();
};


Issue 1
Extensions to HTMLSourceElement may be at risk as discussed in Bug 23827.

partial interface HTMLSourceElement {
  attribute DOMString keySystem;
};

The mediaKeys attribute is the MediaKeys being used when decrypting encrypted media data for this media element.

The setMediaKeys(mediaKeys) method provides the MediaKeys to use when decrypting media data during playback. It must run the following steps:

1. If mediaKeys and the mediaKeys attribute are the same object, return a promise resolved with undefined.

2. Let promise be a new promise.

3. Run the following steps asynchronously:

   1. If mediaKeys is not null, it is already in use by another media element, and the user agent is unable to use it with this element, reject promise with a new DOMException whose name is "QuotaExceededError" and that has the message "The MediaKeys object cannot be used with additional HTMLMediaElements."

   2. If the mediaKeys attribute is not null, run the following steps:

      1. If the user agent or CDM do not support removing the association, return a promise rejected with a new DOMException whose name is "NotSupportedError" and that has the message "The existing MediaKeys object cannot be removed."

      2. If the association cannot currently be removed (i.e. during playback), return a promise rejected with a new DOMException whose name is "InvalidStateError" and that has the message "The existing MediaKeys object cannot be removed at this time."

      3. Stop using the CDM instance represented by the mediaKeys attribute to decrypt media data and remove the association with the media element.

      4. If the preceding step failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   3. If mediaKeys is not null, run the following steps:

      1. Associate the CDM instance represented by mediaKeys with the media element for decrypting media data.

      2. If the preceding step failed, run the following steps:

         1. Set the mediaKeys attribute to null.

         2. Reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

      3. Run the Attempt to Resume Playback If Necessary algorithm on the media element.

         The user agent may choose to skip this step if it knows resuming will fail (i.e. mediaKeys has no sessions).

   4. Set the mediaKeys attribute to mediaKeys.

   5. Resolve promise with undefined.

4. Return promise.

Note: Support for clearing or replacing the associated MediaKeys object during playback is a quality of implementation issue. In many cases it will result in a bad user experience or rejected promise.

Note: As a best practice, applications should create a MediaKeys object and call setMediaKeys() before providing media data (for example, setting the src attribute of the media element). This avoids potential delays in some implementations.

Note: In some implementations, MediaKeySession objects created by createSession() may not fire any events until the MediaKeys object is associated with a media element using setMediaKeys().

The onneedkey event handler for the needkey event must be supported by all HTMLMediaElements as both a content attribute and an IDL attribute.

The waitingFor attribute indicates what the media element is waiting for, if anything (indicated by the waiting and canplay events). This is described in the Encrypted Block Encountered algorithm.

The create(keySystem) method creates a new MediaKeys object for keySystem. It must run the following steps:

1. If keySystem is an empty string, return a promise rejected with a new DOMException whose name is "InvalidAccessError" and that has the message "The keySystem parameter is empty."

2. If keySystem is not one of the Key Systems supported by the user agent, return a promise rejected with a new DOMException whose name is "NotSupportedError" and that has the message "The key system keySystem is not supported." String comparison is case-sensitive.

3. Let promise be a new promise.

4. Run the following steps asynchronously:

   1. Let cdm be the content decryption module corresponding to keySystem.

   2. Load and initialize the cdm if necessary.

   3. If cdm fails to load or initialize, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   4. Let media keys be a new MediaKeys object, and initialize it as follows:

      1. Set the keySystem attribute to keySystem.

   5. Resolve promise with media keys.

5. Return promise.

The keySystem attribute identifies the Key System being used.

The createSession(initDataType, initData, sessionType) method creates a new MediaKeySession object for the initData. It must run the following steps:

The contents of initData are container-specific Initialization Data. initDataType is the initialization data type that indicates how to interpret initData.

Note: User agents and CDMs should not treat sessions created with audio data differently than those created with video data. That is, there is no such thing as an "audio session" or a "video session" - all sessions are used for all media streams processed by cdm.

1. If initDataType is an empty string, return a promise rejected with a new DOMException whose name is "InvalidAccessError" and that has the message "The initDataType parameter is empty."

2. If initData is an empty array, return a promise rejected with a new DOMException whose name is"InvalidAccessError" and that has the message "The initData parameter is empty."

3. If initDataType is not an initialization data type supported by the content decryption module corresponding to the keySystem, return a promise rejected with a new DOMException whose name is "NotSupportedError" and that has the message "The initialization data type initDataType is not supported by the key system." String comparison is case-sensitive.

4. If sessionType is not supported by the content decryption module corresponding to the keySystem, return a promise rejected with a new DOMException whose name is "NotSupportedError" and that has the message "sessionType sessions are not supported by the key system."

5. Let init data be a copy of the contents of the initData parameter.

6. Let promise be a new promise.

7. Run the following steps asynchronously:

   1. If the list of active session Initialization Data for this object includes an entry for the initDataType-init data pair, resolve promise with null.

      In other words, do not create a session if a non-closed session already exists for this init data.

   2. Let request be null.

   3. Let default URL be null.

   4. Let cdm be the cdm loaded in create().

   5. Use the cdm to execute the following steps:

      1. If the init data is not valid for initDataType, reject promise with a new DOMException whose name is "InvalidAccessError" and that has the message "Invalid initialization data."

      2. If the init data is not supported by the cdm, reject promise with a new DOMException whose name is "NotSupportedError" and that has the message "The initialization data is not supported by the key system."

      3. Let request be a request (e.g. a license request) generated based on the init data, which is interpreteted per initDataType, and sessionType.

         If sessionType is "temporary", the request is for a temporary non-persisted license. If sessionType is "persistent", the request is for a persistable license.

         Note: The license server may reject the requested type. It should not issue a different type.

         cdm must not use any stream-specific data, including media data, not provided via the init data.

      4. If the init data indicates a default URL, let default URL be that URL. The URL may be validated and/or normalized.

   6. Let the session ID be a unique Session ID string. It may be obtained from cdm.

   7. Let session be a new MediaKeySession object, and initialize it as follows:

      1. Set the error attribute to null.

      2. Set the sessionId attribute to session ID.

      3. Let expiration be NaN.

      4. Let closed be a new promise.

      5. Let the session type be sessionType.

      6. Let the session initData be the initDataType-init data pair.

   8. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   9. Add an entry for the value of the sessionId attribute to the list of active session IDs for this object.

   10. Add an entry for the initDataType-init data pair to the list of active session Initialization Data for this object.

   11. Run the Queue a "message" Event algorithm on the session, providing request and default URL.

   12. Resolve promise with session.

8. Return promise.

The loadSession(sessionId) method creates a new MediaKeySession object containing the data stored for the sessionId. It must run the following steps:

1. If the content decryption module corresponding to the keySystem attribute does not support loading previous sessions, return a promise rejected with a new DOMException whose name is "NotSupportedError" and that has the message "The operation is not supported by the key system."

2. If sessionId is an empty string, return a promise rejected with a new DOMException whose name is "InvalidAccessError" and that has the message "The sessionId parameter is empty."

3. Let promise be a new promise.

4. Run the following steps asynchronously:

   1. If the list of active session IDs for this object includes an entry for sessionId, resolve promise with null.

      In other words, do not create a session if a non-closed session already exists for this sessionId.

   2. Let expiration time be NaN.

   3. Let request be null.

   4. Let destination URL be null.

   5. Let origin be the origin of the MediaKeys object's Document.

   6. Let cdm be the cdm loaded in create().

   7. Use the cdm to execute the following steps:

      1. If there is no data stored for the sessionId in the origin, resolve promise with undefined.

      2. Let session data be the data stored for the sessionId in the origin. This must not include data from other origin(s) or that is not associated with an origin.

      3. Load the session data.

      4. If the session data indicates an expiration time for the session, let expiration time be the expiration time in milliseconds since 01 January 1970 UTC.

      5. If a message exchange is required:

         1. Let request be a request generated by the CDM based on the session data.

         2. If the session data indicates a destination URL for the request, let destination URL be that URL. The URL may be validated and/or normalized.

   8. Let session be a new MediaKeySession object, and initialize it as follows:

      1. Set the error attribute to null.

      2. Set the sessionId attribute to sessionId.

      3. Let expiration be NaN.

      4. Let closed be a new promise.

      5. Let the session type be "persistent".

   9. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   10. Add an entry for the value of the sessionId attribute to the list of active session IDs for this object.

   11. If the loaded session contains usable keys, run the Usable Keys Changed algorithm on the session.

       The algorithm may also be run later should additional processing be necessary to determine with certainty whether one or more keys is usable.

   12. Run the Update Expiration algorithm on the session, providing expiration time.

   13. If request is not null, run the Queue a "message" Event algorithm on the session, providing request and destination URL.

   14. Resolve promise with session.

5. Return promise.

The setServerCertificate(serverCertificate) method provides a server certificate to be used to encrypt messages to the license server. It must run the following steps:

The contents of serverCertificate are Key System-specific.

Key systems that use such certificates should also support requesting the certificate from the server via an additional round trip. This simplifies interoperability for applications that are not designed to provide certificates to specific key systems.

1. If serverCertificate is an empty array, return a promise rejected with a new DOMException whose name is "InvalidAccessError" and that has the message "The serverCertificate parameter is empty."

2. If the keySystem does not support server certificates, return a promise rejected with a new DOMException whose name is "NotSupportedError" and that has the message "The operation is not supported by the key system."

3. Let certificate be a copy of the contents of the serverCertificate parameter.

4. Let promise be a new promise.

5. Run the following steps asynchronously:

   1. Let cdm be the cdm loaded in create().

   2. Use the cdm to process certificate.

   3. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   4. Resolve promise with undefined.

6. Return promise.

The isTypeSupported(keySystem, initDataType, contentType, capability) method returns whether keySystem is supported with the initDataType, container and codec(s) specified by contentType, and capability.

It must run the following steps:

1. If keySystem is an empty string or contains an unrecognized or unsupported Key System, return the empty string and abort these steps. String comparison is case-sensitive.

2. If the keySystem implementation is not available and usable, return the empty string and abort these steps.

3. Follow the steps for the first matching condition from the following list:

   If keySystem is a value that may be successfully passed to create()

   Let probably result be "probably".

   Otherwise (as may be the case for strings that are only used for discovery)

   Let probably result be "maybe".

4. If initDataType was not provided, follow the steps for the first matching condition from the following list and abort these steps:

   If the user agent is not confident that the keySystem implementation is available and usable

   Return "maybe".

   Otherwise

   Return probably result.

5. If initDataType is an empty string or contains an unrecognized or unsupported initialization data type, return the empty string and abort these steps. String comparison is case-sensitive.

6. If initDataType is not an initialization data type supported by the the keySystem implementation, return the empty string and abort these steps.

7. If the keySystem implementation supporting initDataType is not available and usable, return the empty string and abort these steps.

8. If contentType was not provided, follow the steps for the first matching condition from the following list and abort these steps:

   If the user agent is not confident that the keySystem implementation supporting initDataType is available and usable

   Return "maybe".

   Otherwise

   Return probably result.

9. If contentType is an empty string or contains an invalid or unrecognized MIME type, return the empty string and abort these steps.

10. Let container be the container type specified by contentType.

11. Let parameters be the RFC 6381 parameters, if any, specified by contentType.

12. Let media types be the set of media types specified by parameters. (For example, all of the codecs.) It may be empty. The case-sensitivity of string comparisons is determined by the appropriate RFC or other specification. (Case-sensitive string comparison is recommended because RFC 6381 says, "Values are case sensitive" for some formats.)

13. If the user agent does not support container, return the empty string and abort these steps. The case-sensitivity of string comparisons is determined by the appropriate RFC. (Per RFC 6838, "Both top-level type and subtype names are case-insensitive.")

14. If the user agent and keySystem implementation do not support playback of encrypted media data for all media types, return the empty string and abort these steps.

15. If capability was not provided, follow the steps for the first matching condition from the following list and abort these steps:

    If the user agent is not confident that the keySystem implementation supporting initDataType is available and usable to decrypt and enable playback of support playback of encrypted media data for all media types

    Return "maybe".

    If the user agent is not did not recognize one or more parameters

    Return "maybe".

    Otherwise

    Return probably result.

16. If capability is an empty string, return the empty string and abort these steps.

17. If the keySystem implementation does not support capability, return the empty string and abort these steps. String comparison is case-sensitive.

18. Follow the steps for the first matching condition from the following list:

    If the user agent is not confident that the keySystem implementation supporting initDataType is available and usable to decrypt and enable playback of support playback of encrypted media data for all media types as specified by capability

    Return "maybe".

    If the user agent is not did not recognize one or more parameters

    Return "maybe".

    Otherwise

    Return probably result.

The error attribute is a MediaKeyError representing the current error state of the session. It is null if there is no error.

The sessionId attribute is the Session ID for this object and the associated key(s) or license(s).

The expiration attribute is the time, in milliseconds since since 01 January, 1970 UTC, after which the the key(s) in the session will no longer be usable to decrypt media data, or NaN if no such time exists, as determined by the CDM.

The closed attribute signals when object becomes closed as a result of the Session Close algorithm being run. This promise can only be fulfilled and is never rejected.

The update(response) method provides messages, including licenses, to the CDM. It must run the following steps:

The contents of response are keySystem-specific.

1. If response is an empty array, return a promise rejected with a new DOMException whose name is "InvalidAccessError" and that has the message "The response parameter is empty."

2. Let message be a copy of the contents of the response parameter.

3. Let promise be a new promise.

4. Run the following steps asynchronously:

   1. Let cdm be the cdm loaded in create().

   2. Let request be null.

   3. Let destination URL be null.

   4. Use the cdm to execute the following steps:

      1. If the format of message is invalid in any way, reject promise with a new DOMException whose name is "InvalidAccessError" and that has the message "Invalid response format."

      2. Process message

         If message contains a license, key(s), or similar session data, follow the stipulation for the first matching condition from the following list:

         If sessionType is "temporary" and the license does not specify it should be stored

         Do not store the license, key(s), or similar session data contained in message.

         If sessionType is "persistent" and the license permits storage

         Store the license, key(s), or similar session data contained in message.

         Otherwise

         Fail with an appropriate error name and message.

         Note: When message contains key(s) and/or related data, cdm will likely cache the key and related data indexed by key ID.

         Note: The replacement algorithm within a session is Key System-dependent.

         Note: Keys from different sessions should be cached independently such that closing one session does not affect keys in other sessions, even if they have overlapping key IDs.

         Note: It is recommended that CDMs support a standard and reasonably high minimum number of keys per MediaKeySession object, including a standard replacement algorithm, and a standard and reasonably high minimum number of MediaKeySession objects. This enables a reasonable number of key rotation algorithms to be implemented across user agents and may reduce the likelihood of playback interruptions in use cases that involve various streams in the same element (i.e. adaptive streams, various audio and video tracks) using different keys.

      3. If the set of usable keys changed, run the Usable Keys Changed algorithm on the session.

         The algorithm may also be run later should additional processing be necessary to determine with certainty whether one or more keys is usable.

      4. If the expiration time for the session changed, run the Update Expiration algorithm on the session, providing the new expiration time.

      5. If another message needs to be sent to the server, execute the following steps:

         1. Let request be that message.

         2. If there is a specific destination URL for the message, let destination URL be that URL. The URL may be validated and/or normalized.

   5. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   6. If request is not null, run the Queue a "message" Event algorithm on the session, providing request and destination URL.

   7. Resolve promise with undefined.

5. Return promise.

The close() method allows an application to indicate that it no longer needs the session and the CDM should release any resources associated with this object and close it. The returned promise is resolved when the request has been processed, and the closed attribute promise is resolved when the session is closed. It must run the following steps:

1. If the Session Close algorithm has been run on this object, return a promise fulfilled with undefined.

2. Let promise be a new promise.

3. Run the following steps asynchronously:

   1. Let cdm be the cdm loaded in create().

   2. Use the cdm to execute the following steps:

      1. Process the close request.

         Do not remove stored session data.

      2. If the previous step caused the session to be closed, run the Session Close algorithm on this object.

   3. Resolve promise with undefined.

4. Return promise.

The remove() method allows an application to remove stored session data associated with this object. It must run the following steps:

1. If the session type is not "persistent", return a promise rejected with a new DOMException whose name is "InvalidAccessError" and that has the message "The operation is not supported on session type sessions."

2. If the Session Close algorithm has been run on this object, return a promise rejected with a new DOMException whose name is "InvalidStateError" and that has the message "The session is closed."

3. Let promise be a new promise.

4. Run the following steps asynchronously:

   1. Let cdm be the cdm loaded in create().

   2. Use the cdm to execute the following steps:

      1. Process the remove request.

         This may involve exchanging message(s) with the application.

         Unless this step fails, the CDM must have cleared all stored session data associated with this object, including the sessionId, before proceeding to the next step. (A subsequent call to loadSession() with sessionId would fail because there is no data stored for the sessionId.)

   3. Run the following steps asynchronously once the above step has completed:

      1. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

      2. Run the Session Close algorithm on this object.

      3. Resolve promise with undefined.

5. Return promise.

The getUsableKeyIds() method allows an application to get the key IDs for keys in the session that the CDM knows are currently usable to decrypt media data. It must run the following steps:

1. Let promise be a new promise.

2. Run the following steps asynchronously:

   1. Let cdm be the cdm loaded in create().

   2. Use the cdm to execute the following steps:

      1. Let usable key ids be a list of the key IDs for keys in the session that the CDM knows are currently usable to decrypt media data. usable key ids must not contain IDs for keys that may not currently be usable. Each element must be unique.

   3. If the preceding step failed, reject promise with a new DOMException whose name is the appropriate error name and that has an appropriate message.

   4. Resolve promise with a new Sequence object, each element of which contains one element of usable key ids.

The keysystem content attribute is added to HTMLSourceElement. It specifies the Key System to be used with the media resource.

The keySystem IDL attribute is added to HTMLSourceElement. It must reflect the keysystem content attribute.

The resource selection algorithm is modified to check the keysystem attribute after the existing step 5 of the Otherwise branch of step 9:

6. ⌛ If candidate has a keysystem attribute whose value represents a Key System that the user agent knows it cannot use with type, then end the synchronous section, and jump down to the failed step below.

2.1. Exceptions

The methods report errors by rejecting the the returned promise with a DOMException. The following DOMException names from DOM4 are used with messages as shown in the following table. In cases where the exact name is not specified in the algorithm, the message may differ to reflect the actual error.

2.2. MediaKeyError

2.2.1. Interface

[Constructor(DOMString name, unsigned long systemCode, optional DOMString message = "")]
interface MediaKeyError : DOMException {
  readonly attribute unsigned long systemCode;
};

2.2.2. Error Names

The tables below list all the allowed error names for the name property along with a description. The message may be key system-specific.

The following DOMException names from DOM4 may be used as shown in the following table:

The following new DOMException names are defined by this specification:

2.3 Media Element Restrictions

This section is non-normative.

Media data processed by a CDM may not be available through Javascript APIs in the usual way (for example using the CanvasRenderingContext2D drawImage() method and the AudioContext MediaElementAudioSourceNode). This specification does not define conditions for such non-availability of media data, however, if media data is not available to Javascript APIs then these APIs may behave as if no media data was present at all.

Where media rendering is not performed by the UA, for example in the case of a hardware protected media pipeline, then the full set of HTML rendering capabilities, for example CSS Transforms, may not be available. One likely restriction is that video media may be constrained to appear only in rectangular regions with sides parallel to the edges of the window and with normal orientation.

3. Events

3.1. Event Definitions

[Constructor(DOMString type, optional MediaKeyNeededEventInit eventInitDict)]
interface MediaKeyNeededEvent : Event {
  readonly attribute DOMString initDataType;
  readonly attribute ArrayBuffer? initData;
};

dictionary MediaKeyNeededEventInit : EventInit {
  DOMString initDataType = "";
  ArrayBuffer? initData = null;
};

[Constructor(DOMString type, optional MediaKeyMessageEventInit eventInitDict)]
interface MediaKeyMessageEvent : Event {
  readonly attribute ArrayBuffer message;
  readonly attribute DOMString? destinationURL;
};

dictionary MediaKeyMessageEventInit : EventInit {
  ArrayBuffer message = ArrayBuffer();
  DOMString? destinationURL = null;
};

event . initDataType

Returns a string indicating the initialization data type of the Initialization Data related to the event.

event . initData

Returns the Initialization Data related to the event.

event . message

Returns the message (i.e. license request) to send.

event . destinationURL

Returns the URL to which the message should be sent.

3.2. Event Summary

This section is non-normative.

The following event is fired at HTMLMediaElement.

The following events are fired at MediaKeySession.

4. Algorithms

4.1. Initialization Data Encountered

The following steps are run when the media element encounters Initialization Data in the media data during the resource fetch algorithm:

1. Let initDataType be the empty string.

2. Let initData be null.

3. If the media data is CORS-same-origin, run the following steps:

   1. Let initDataType be the string representing the initialization data type of that initialization data.

   2. Let initData be that initialization data.

4. Queue a task to fire a simple event named needkey at the media element.

   The event is of type MediaKeyNeededEvent and has:

   • initDataType = initDataType
     initData = initData

   Firing this event allows the application to begin acquiring the key process before it is needed.

   Note that readyState is not changed and no algorithms are aborted. This event merely provides information.

   Note that if the media is not CORS-same-origin then the initData will be null. This allows applications that can retrieve initData from an alternative source to continue. Applications with no way to retrieve initData may wish to consider aborting playback in this case.

5. Continue Normal Flow: Continue with the existing media element's resource fetch algorithm.

4.2. Encrypted Block Encountered

The following steps are run when the media element encounters a block (i.e. frame) of encrypted media data during the resource fetch algorithm:

1. If the media element's mediaKeys attribute is not null, run the following steps:

   1. Let media keys be the MediaKeys object referenced by that atribute.

   2. Let cdm be the cdm loaded during the initialization of the media keys.

   3. If there is at least one MediaKeySession created by the media keys on which the Session Close algorithm has not been run, run the following steps:

      This check ensures the cdm has finished loading and is a prequisite for a matching key being available.

      1. Let the block key ID be the key ID of the current block (as specified by the container).

      2. Use the cdm to execute the following steps:

         1. Let available keys be the union of keys in sessions that were created by the media keys.

         2. Follow the steps for the first matching condition from the following list:

            If any of the available keys corresponds to the block key ID and is usable

            Run the following steps:

            1. Let block key be the matching key.

               Note: If multiple sessions contain a usable key for the block key ID, which key to use is Key System-dependent.

            2. Use the cdm to decrypt the block using block key.

            3. Follow the steps for the first matching condition from the following list:

               If decryption fails

               Abort the media element's resource fetch algorithm, run the steps to report a MEDIA_ERR_DECODE error, and abort these steps.

               Otherwise

               Run the following steps:

               1. If the waitingFor attribute on the media element is "key", set the waitingFor attribute on the media element to "none".

               2. Abort these steps and process the decrypted block as normal. (Decode the block.)

               Note: Not all decryption problems (i.e. using the wrong key) will result in a decryption failure. In such cases, no error is fired here but one may be fired during decode.

            If any of the available keys corresponds to the block key ID and is unusable

            Run the following steps:

            1. Let session be the MediaKeySession object associated with that session.

            2. Run the Queue an "error" Event algorithm on the session, providing the appropriate error name and system code value, if provided, and 0 otherwise.

            3. Abort these steps.

            Otherwise (there is no key for the block key ID in any session)

            Continue.

2. There is no usable key for the block. Run the following steps:

   1. Run the Queue a "waiting" Event algorithm on the media element.

   2. Wait for a signal to resume playback.

The following steps are added to readyState change algorithms in Playing the media resource:

• If a readyState change queues a task to fire a waiting event, the user agent must also set the waitingFor attribute on the Media Element to "data".
• If a readyState change queues a task to fire a canplay event, the user agent must also set the waitingFor attribute on the Media Element to "none".

4.3. Queue a "message" Event

The Queue a "message" Event algorithm is run when the CDM needs to queue a message event to a MediaKeySession object. Requests to run this algorithm include a target MediaKeySession object, a request, and a destination URL.

The following steps are run:

1. Let the session be the specified MediaKeySession object.

2. Queue a task to fire a simple event named message at the session.

   The event is of type MediaKeyMessageEvent and has:

   • message = the specified request
     destinationURL = the specified destination URL

4.4. Queue an "error" Event

The Queue an "error" Event algorithm is run when the CDM needs to queue an error event to a MediaKeySession object. Requests to run this algorithm include a target MediaKeySession object, an error name, and a system code.

The following steps are run:

1. Let the session be the specified MediaKeySession object.

2. Create a new MediaKeyError object with the following attributes:

   • name = error name
     systemCode = system code

3. Set the session's error attribute to the error object created in the previous step.

4. Queue a task to fire a simple event named error at the session.

4.5. Usable Keys Changed

The Usable Keys Changed algorithm is run when the CDM changes the set of keys in the session that may be used for decryption. This can happen as the result of an update() call or some other event. Requests to run this algorithm include a target MediaKeySession object.

The following steps are run:

1. Let the session be the associated MediaKeySession object.

2. Queue a task to fire a simple event named keyschange at the session.

3. Run the Attempt to Resume Playback If Necessary algorithm on each of the media element(s) whose mediaKeys attribute is the MediaKeys object that created the session.

   The user agent may choose to skip this step if it knows resuming will fail (i.e. no additional keys became available).

4.6. Update Expiration

The Update Expiration algorithm is run when the CDM changes the expiration time of a session. This can happen as the result of an update() call or some other event. Requests to run this algorithm include a target MediaKeySession object and the new expiration time, which may be NaN.

The following steps are run:

1. Let the session be the associated MediaKeySession object.

2. Let expiration time be NaN.

3. If the new expiration time is not NaN, let expiration time be the new expiration time in milliseconds since 01 January 1970 UTC.

4. Set the session's expiration attribute to expiration time.

4.7. Session Close

The Session Close algorithm is run when the CDM closes the session associated with a MediaKeySession object.

The CDM may close a session at any point, such as in response to a close() call, when the session is no longer needed, or when system resources are lost. Keys in other sessions should be unaffected, even if they have overlapping key IDs.

The following steps are run:

1. Let the session be the associated MediaKeySession object.

2. Remove the entry for the value of the session's sessionId attribute from the list of active session IDs for the MediaKeys object that created the session.

3. If the session initData of the session is not empty, remove its entry from the list of active session Initialization Data for the MediaKeys object that created the session.

4. Let promise be the closed attribute of the session.

5. Resolve promise with undefined.

4.8. Queue a "waiting" Event

The Queue a "waiting" Event algorithm is run when the CDM needs to queue a waiting event to a HTMLMediaElement object. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

1. Let the media element be the specified HTMLMediaElement object.

2. If the waitingFor attribute on the media element is not "key", run the following steps:

   1. Set the waitingFor attribute on the media element to "key".

   2. Queue a task to fire a simple event named timeupdate at the media element.

   3. Queue a task to fire a simple event named waiting at the media element.

3. Suspend playback.

4.9. Attempt to Resume Playback If Necessary

The Attempt to Resume Playback If Necessary algorithm is run when one or more keys becomes available. If playback is blocked waiting for a key, it resumes playback if a necessary key has been provided. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

1. Let the media element be the specified HTMLMediaElement object.

2. If the waitingFor attribute on the media element is not "key", abort these steps.

3. Attempt to resume the resource fetch algorithm by running the Encrypted Block Encountered algorithm.

4. If the user agent can advance the current playback position in the direction of playback, queue a task to fire a simple event named canplay at the media element.

   Otherwise, the waitingFor attribute on the media element must not be "none".

5. Simple Decryption

All user agents must support the simple decryption capabilities described in this section regardless of whether they support a more advanced CDM. This ensures that there is a common baseline level of protection that is guaranteed to be supported in all user agents, including those that are entirely open source. Thus, content providers that need only basic protection can build simple applications that will work on all platforms without needing to work with any content protection providers.

5.1. Clear Key

The "org.w3.clearkey" Key System uses plain-text clear (unencrypted) key(s) to decrypt the source. No additional client-side content protection is required. This Key System is described below.

5.1.1. Capabilities

The following describe how Clear Key supports key system-specific capabilities:

• The setMediaKeys() method: Implementations may support associating the MediaKeys object with more than one HTMLMediaElement.

• The setServerCertificate() method: Not supported.

• The isTypeSupported() method: There are no supported capability values.

• The "persistent" SessionType, including the loadSession() and remove() methods: Implementations may support these.

5.1.2. Behavior

The following describe how Clear Key implements key system-specific behaviors:

• In the createSession() algorithm:

  • The generated request is a JSON object encoded in UTF-8 as described in License Request Format.

  • The request is generated by extracting the key IDs from the init data.

  • The "type" member value is the value of the sessionType parameter.

• The sessionId attribute is a numerical value representable by a 32-bit integer.

• The expiration attribute is always NaN.

• In the update() algorithm:

  • The response parameter is a JWK Set as described in License Format.

  • message is considered invalid if it is not a valid JWK Set with at least one valid JWK key of a valid length for the media type.

• The getUsableKeyIds() method always returns all key IDs that have been provided via update().

• Initialization Data: Implementations may support any combination of registered and Initialization Data types. Implementations should support the "keyids" type and other types appropriate for content types supported by the user agent.

5.1.3. License Request Format

This section describes the format of the license request provided to the application via the message attribute of the message event.

The format is a JSON object containing the following members:

"kids"

An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.

"type"

The requested SessionType

When contained in the ArrayBuffer message attribute of a MediaKeyMessageEvent object, the JSON string is encoded in UTF-8 as specified in the Encoding specification. Applications may decode the contents of the ArrayBuffer to a JSON string using the TextDecoder interface.

5.1.3.1. Example

This section is non-normative.

The following example is a license request for a temporary license for two key IDs. (Line breaks are for readability only.)

{
  "kids": 
    [
     "67ef0gd8pvfd0",
     "77ef0gd8pvfd0"
    ],
  "type":"temporary"
}

5.1.4. License Format

This section describes the format of the license to be provided via the response parameter of the update() method.

The format is a JSON Web Key (JWK) Set containing representation of the symmetric key to be used for decryption, as defined in the IETF Internet-draft JSON Web Key (JWK) specification.

For each JWK in the set, the parameter values are as follows:

"kty" (key type)

"oct" (octet sequence)

"alg" (algorithm)

"A128KW" (AES key wrap using a 128-bit key)

"k" (key value)

The base64url encoding of the octet sequence containing the symmetric key value

"kid" (key ID)

The base64url encoding of the octet sequence containing the key ID value

The JSON object may have an optional "type" member value, which may be any of the SessionType values. If not specified, the default value of "temporary" is used. The update() algorithm compares this value to the sessionType.

When passed to the update() method as the ArrayBuffer response parameter, the JSON string must be encoded in UTF-8 as specified in the Encoding specification. Applications may encode the JSON string using the TextEncoder interface.

5.1.4.1. Example

This section is non-normative.

The following example is a JWK Set containing a single symmetric key. (Line breaks are for readability only.)

{
  "keys": 
    [{
      "kty":"oct",
      "alg":"A128KW",
      "k":"GawgguFyGrWKav7AX4VKUg"
      "kid":"67ef0gd8pvfd0",
    }],
  "type":"temporary"
}

5.1.5. Using base64url

This section is non-normative.

For more information on base64url and working with it, see the Base64url Encoding entry in the Terminology section and Notes on implementing base64url encoding without padding of the JSON Web Signature (JWS) specification. Specifically, there is no '=' padding, and the characters '-' and '_' must be used instead of '+' and '/', respectively.

6. Security Considerations

7. Privacy Considerations

8. Examples

This section and its subsections are non-normative.

This section contains example solutions for various use cases using the proposed extensions. These are not the only solutions to these use cases. Video elements are used in the examples, but the same would apply to all media elements. In some cases, such as using synchronous XHR, the examples are simplified to keep the focus on the extensions.

8.1. Source and Key Known at Page Load (Clear Key)

In this simple example, the source file and clear-text license are hard-coded in the page. Only one session will ever be created.

<script>
  function load() {
    var video = document.getElementById("video");

    if (!video.mediaKeys) {
      var promise = MediaKeys.create("org.w3.clearkey");
      promise.catch(
        console.error.bind(console, "Unable to create MediaKeys")
      );
      promise.then(
        function(createdMediaKeys) {
          return video.setMediaKeys(createdMediaKeys);
        }
      ).catch(
        console.error.bind(console, "Unable to set MediaKeys")
      );
      promise.then(
        function(createdMediaKeys) {
          var initData = new Uint8Array([ ... ]);
          return createdMediaKeys.createSession("webm", initData);
        }
      ).then(
        function(keySession) {
          keySession.addEventListener("message", handleMessage, false);
        }
      ).catch(
        console.error.bind(console, "Unable to create key session")
      );
    }
  }

  function handleMessage(event) {
    var keySession = event.target;

    var license = new Uint8Array([ ... ]);
    keySession.update(license).catch(
      console.error.bind(console, "update() failed")
    );
  }
</script>

<body onload="load()">
  <video src="foo.webm" autoplay id="video"></video>
</body>

8.2. Selecting a Supported Key System and Using Initialization Data from the "needkey" Event

This example selects a supported Key System using the isTypeSupported() method then uses the Initialization Data from the media data to generate the license request and send it to the appropriate license server. One of the supported key systems uses a serverCertificate, which is provided proactively.

<script>
  var keySystem;
  var licenseUrl;
  var serverCertificate;

  function selectKeySystem() {
    if (MediaKeys.isTypeSupported("com.example.somesystem", "webm", "video/webm; codecs='vp8, vorbis'")) {
      licenseUrl = "https://license.example.com/getkey"; // OR "https://example.<My Video Site domain>"
      keySystem = "com.example.somesystem";
      serverCertificate = new Uint8Array([ ... ]);
    } else if (MediaKeys.isTypeSupported("com.foobar", "webm", "video/webm; codecs='vp8, vorbis'")) {
      licenseUrl = "https://license.foobar.com/request";
      keySystem = "com.foobar";
    } else {
      throw "Key System not supported";
    }
  }

  function handleKeyNeeded(event) {
    var video = event.target;
    if (video.mediaKeysObject === undefined) {
      selectKeySystem();
      video.mediaKeysObject = null; // Prevent entering this path again.
      video.pendingSessionData = []; // Will store all initData until the MediaKeys is ready.
      MediaKeys.create(keySystem).then(
        function(createdMediaKeys) {
          video.mediaKeysObject = createdMediaKeys;

          if (serverCertificate)
            createdMediaKeys.setServerCertificate(serverCertificate);

          for (var i = 0; i < video.pendingSessionData.length; i++) {
            var data = video.pendingSessionData[i];
            createSession(video.mediaKeysObject, data.initDataType, data.initData);
          }
          video.pendingSessionData = [];

          return video.setMediaKeys(createdMediaKeys);
        }
      ).catch(
        console.error.bind(console, "Unable to create or use new MediaKeys")
      );
    }
    addSession(video, event.initDataType, event.initData);
  }

  function addSession(video, initDataType, initData) {
    if (video.mediaKeysObject) {
      createSession(video.mediaKeysObject, initDataType, initData);
    } else {
      video.pendingSessionData.push({initDataType: initDataType, initData: initData});
    }
  }

  function createSession(mediaKeys, initDataType, initData) {
    mediaKeys.createSession(initDataType, initData).then(
      function(keySession) {
        if (keySession) {
          keySession.addEventListener("message", licenseRequestReady, false);
        } else {
          console.log("A session already exists for the initData");
        }
      }
    ).catch(
      console.error.bind(console, "Unable to create or initialize key session")
    );
  }

  function licenseRequestReady(event) {
    var request = event.message;

    var xmlhttp = new XMLHttpRequest();
    xmlhttp.keySession = event.target;
    xmlhttp.open("POST", licenseUrl);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4) {
        var license = new Uint8Array(xmlhttp.response);
        xmlhttp.keySession.update(license).catch(
          console.error.bind(console, "update() failed")
        );
      }
    }
    xmlhttp.send(request);
  }
</script>

<video src="foo.webm" autoplay onneedkey="handleKeyNeeded(event)"></video>

8.3. Create MediaKeys Before Loading Media

Initialization is much simpler if needkey events do not need to be handled during MediaKeys initialization. This can be accomplished either by providing the Initialization Data in other ways or setting the source after the MediaKeys object has been created. This example does the latter.

<script>
  var keySystem;
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See the previous example for implementations of these functions.
  function selectKeySystem() { ... }
  function createSession(mediaKeys, initDataType, initData) { ... }
  function licenseRequestReady(event) { ... }

  function handleKeyNeeded(event) {
    createSession(mediaKeys, event.initDataType, event.initData);
  }

  selectKeySystem();
  MediaKeys.create(keySystem).then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      video.src = "foo.webm";
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, "Unable to create or initialize key session")
  );
</script>

<video id="v" autoplay onneedkey="handleKeyNeeded(event)"></video>

8.4. Using All Events

This is a more complete example showing all events being used.

Note that handleMessage() could be called multiple times, including in response to the update() call if multiple round trips are required and for any other reason the Key System might need to send a message.

<script>
  var keySystem;
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See previous examples for implementations of these functions.
  function selectKeySystem() { ... }
  function handleKeyNeeded(event) { ... }

  // This replaces the implementation in the previous example.
  function createSession(mediaKeys, initDataType, initData) {
    mediaKeys.createSession(initDataType, initData).then(
      function(keySession) {
        if (!keySession)
          return; // A session already exists for the initData.
        keySession.addEventListener("message", handleMessage, false);
        keySession.addEventListener("keyschange", handleKeysChange, false);
        keySession.addEventListener("error", handleError, false);
        keySession.closed.then(
          console.log.bind(console, "Session closed")
        );
      }
    ).catch(
      console.error.bind(console, "Unable to create or initialize key session")
    );
  }

  function handleMessageResponse(keySession, response) {
    var license = new Uint8Array(response);
    keySession.update(license).catch(
      function(err) {
        console.error("update() failed: " + err);
      }
    );
  }

  function sendMessage(message, keySession) {
    xmlhttp = new XMLHttpRequest();
    xmlhttp.keySession = keySession;
    xmlhttp.open("POST", licenseUrl);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4)
        handleMessageResponse(xmlhttp.keySession, xmlhttp.response);
    }
    xmlhttp.send(message);
  }

  function handleMessage(event) {
    sendMessage(event.message, event.target);
  }

  function handleKeysChange(event) {
    event.target.getUsableKeyIds().then(
      function(keyIdSequence) {
        // Process keyIdSequence and respond appropriately.
      }
    ).catch(
      console.error.bind(console, "Failed handling usable keys change")
    );
  }

  function handleError(event) {
    // Report event.target.error.name and event.target.error.systemCode,
    // and do some bookkeeping with event.target.sessionId if necessary.
  }

  selectKeySystem();
  MediaKeys.create(keySystem).then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      video.src = "foo.webm";
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, "Unable to create or use new MediaKeys")
  );
</script>

<video id="v" autoplay onneedkey="handleKeyNeeded(event)"></video>

8.5. Stored License

This example requests a persistent license for future use and stores it. It also provides functions for later retrieving the license and for destroying it.

<script>
  var keySystem;
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See the previous examples for implementations of these functions.
  function selectKeySystem() { ... }
  function sendMessage(message, keySession) { ... }
  function handleMessage(event) { ... }
  function handleError(event) { ... }

  // Called if the application does not have a stored sessionId for the media resource.
  function createSession(mediaKeys, initDataType, initData) {
    mediaKeys.createSession(initDataType, initData, "persistent").then(
      function(keySession) {
        if (!keySession)
          return; // A session already exists for the initData.
        keySession.addEventListener("message", handleMessage, false);
        keySession.addEventListener("error", handleError, false);
        keySession.closed.then(
          function() {
            console.log("Session " + this.sessionId + " closed");
          }.bind(keySession)        
        );
        // Store keySession.sessionId in the application.
      }
    ).catch(
      console.error.bind(console, "Unable to create or initialize a persistable key session")
    );
  }

  // Called if the application has a stored sessionId for the media resource.
  function loadStoredSession(mediaKeys, sessionId) {
    mediaKeys.loadSession(sessionId).then(
      function(keySession) {
        if (!keySession) {
          console.error("No stored session with the ID " + sessionId + " was found.");
          // The application should remove its record of |sessionId|.
          return;
        }
        keySession.addEventListener("message", handleMessage, false);
        keySession.addEventListener("error", handleError, false);
        keySession.closed.then(
          console.log.bind(console, "Session closed")
        );
      }
    ).catch(
      console.error.bind(console, "Unable to load or initialize the stored session with the ID " + sessionId)
    );
  }

  // Called when the application wants to stop using the session without removing the stored license.
  function closeSession(keySession) {
    keySession.close();
  }

  // Called when the application wants to remove the stored license.
  // The stored session data has not been completely removed until the promise returned by remove() is fulfilled.
  // The remove() call may initiate a series of messages to/from the server that must be completed before this occurs.
  function removeStoredSession(keySession) {
    keySession.remove().then(
      function() {
        console.log("Session " + this.sessionId + " removed");
        // The application should remove its record of this.sessionId.
      }.bind(keySession)
    ).catch(
      console.error.bind(console, "Failed to remove the session")
    );
  }

  // This replaces the implementation in the previous example.
  function handleMessageResponse(keySession, response) {
    var license = new Uint8Array(response);
    keySession.update(license).then(
      function() {
        // If this was the last required message from the server, the license is
        // now stored. Update the application state as appropriate.
      }
    ).catch(
      console.error.bind(console, "update() failed")
    );
  }

  selectKeySystem();
  MediaKeys.create(keySystem).then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, "Unable to create or use new MediaKeys")
  );
</script>

<video id="v" src="foo.webm" autoplay></video>

9. Revision History