Second Screen Working Group Charter

This charter has been replaced by a newer version.

The mission of the Second Screen Working Group is to provide specifications that enable web pages to use secondary screens (presentation displays) to display web content.

Join the Second Screen Working Group

Start date	11 December 2019
End date	31 December 2021
Charter extension	See Change History
Chairs	Anssi Kostiainen
Team Contacts	François Daoust (0.1 FTE)
Meeting Schedule	Teleconferences: topic-specific calls may be held Face-to-face: we will meet during the W3C's annual Technical Plenary week; other additional F2F meetings may be scheduled (up to 2 per year) IRC: active participants use the #webscreens W3C IRC channel during F2F meetings and teleconferences.

Goals

Web applications are available on an ever expanding array of devices including e-book readers, phones, tablets, laptops, auto displays, and electronic signs. A variety of mechanisms allow these devices to use secondary audio and video presentation devices available in the local environment, attached by wired connections or remotely with wireless, peer-to-peer media.

Common attachment methods include video ports like VGA, DisplayPort or HDMI, or via wireless protocols such as Miracast, WiDi, AirPlay, Bluetooth, and Google Cast. Wireless presentation displays may be available on a local area network, or over the Internet (brokered by a cloud service). In addition to displays like monitors and TVs, wireless speakers can serve as secondary devices for rendering Web content. General purpose PCs and laptops can also serve as secondary presentation displays.

For many of these displays, the operating system hides how the display is attached and provides ways for native applications to render media on them. Native applications can easily use additional presentation displays without having to know the details of the connection technology.

The Second Screen Working Group aims at defining simple APIs and an open suite of network protocols (specified as an application of existing IETF protocols) that allow web applications to present and control web content on one or more presentation displays and speakers.

Scope

The scope of this Working Group is to define:

APIs that allow a web application to request display of web content on a nearby presentation display, with a means to communicate with and control the web content from the initiating page and other authorized pages;
A suite of network protocols that allow user agents to implement the APIs in an interoperable fashion for browsers and presentation displays connected via the same local area network.

Pages may become authorized to control the displayed web content through explicit user permission, a token provided by the API, or other facilities provided by the user agent. The APIs will hide the details of the underlying connection technologies and use familiar, common APIs for messaging among authorized pages and the web content shown on the presentation display. Web content may comprise an HTML document; parts of an HTML document; web media types such as images, audio, video; or application-specific media. The presentation of application-specific media is known to the controlling user agent and the presentation display, but not necessarily to a generic HTML user agent.

For a requested piece of web content, the user agent is responsible for determining which presentation displays are compatible with that content. The API will provide the means for the web application to identify whether rendering the web content is likely to be successful, i.e. whether at least one presentation display is available that is capable of rendering the web content.

The API is agnostic with regard to the display technology used. The user agent may ask the presentation display to render the web content, or the user agent may render the web content itself and send the resulting audio and video to the presentation display using whatever means the operating system provides. From the web application's point of view, which device is responsible for rendering the web content is an implementation detail.

Presenting web content on a presentation display creates a presentation connection between the web application and the web content. Web applications should be able to create multiple presentation connections to control web content shown on multiple presentation displays. Some web content, such as HTML5 documents, can be controlled from multiple web applications simultaneously. Synchronization of web content among multiple connections may be possible, but is not defined by the specifications in this group.

The suite of network protocols will cover required steps for two user agents to implement the APIs: discovery, authentication, transport, and messaging (including API control messages and messages for streaming media between agents). The suite will reuse and configure existing IETF protocols for each of these steps. This Working Group will work with the IETF to assess whether parts of the protocol suite may apply to broader scenarios than the ones envisioned for the APIs. If that is the case, those parts may be further developed in the IETF.

This Working Group will not mandate network protocols for sharing web content between user agents and presentation displays. The APIs will informatively reference the protocol suite.

The specifications produced by this Working Group will include security and privacy considerations. In particular, the user must always be in control of privacy-sensitive information that may be conveyed through the APIs, such as the visibility or access to presentation displays, or the URLs of the web content to be presented.

Members of the Working Group should review other Working Groups' deliverables that are identified as being relevant to the Working Group's mission.

Out of Scope

The specifications defined by this Working Group abstract away the means of connecting and different connection technologies. For example, the following are out of scope:

Lower level APIs that expose features of existing connection technologies;
How presentation displays are connected to the primary device (e.g. Video Port, HDMI, WiDi, Miracast, AirPlay);
How the user agent prepares and sends the screen contents to the presentation display.

This Working Group will reuse and configure existing network protocols to create an open suite of network protocols suitable for the APIs. As such, the following are out of scope for the Working Group:

Any new feature in existing IETF protocols normatively referenced by the suite of network protocols;
Any new protocol for discovery, authentication, transport and messaging;
Any protocol not required to implement the APIs developed by this Working Group.

Input methods, such as using a TV remote as a pointer or clicker, are out of scope of the Working Group.

This Working Group will not define or mandate any video or audio codecs.

Deliverables

Draft state indicates the state of the deliverable at the time of the call for participation. Expected completion indicates when the deliverable is projected to become a Recommendation, or otherwise reach a stable state.

Normative Specifications

The Working Group will deliver at least the following specifications:

Presentation API

An API that allows a web application to request display of web content on a connected display, with a means to communicate with and control the web content from the initiating page and other authorized pages.

Draft state: CR / Stable

Expected completion: Q4 2021 — The Working Group is awaiting satisfaction of the Success Criteria, which require two interoperable implementations of the Presentation API. The Working Group will also await demonstration of interoperability among multiple browsers and multiple presentation displays before moving the specification to Proposed Recommendation.

Reference Draft: https://www.w3.org/TR/2017/CR-presentation-api-20170601/
Associated Call for Exclusion on 19 October 2017 ended on 31 July 2017
Produced under Working Group Charter: https://www.w3.org/2014/secondscreen/charter-2016.html

The Open Screen Protocol will be the basis for demonstrating interoperability between browsers and devices. Two implementations based on it would satisfy those criteria. The charter timeline provides additional time for Open Screen Protocol implementations to be completed and the Success Criteria to be met.

A second version of the Presentation API that integrates features the Working Group resolved not to include in the first version in the interest of time, and also feedback from Web developers on the first version, will first be incubated and matured in an appropriate Community Group. This Working Group expects to bring such features out of incubation through rechartering, when the criteria for moving the current Presentation API to Proposed Recommendation have been met.

Additional features will be considered for the Presentation API to align it with the work on the Open Screen Protocol, based on implementation experience with that protocol.

Additional features will also be considered to improve compatibility with the Remote Playback API and presentation of additional media types that are supported by the Open Screen Protocol.

All API changes will be incubated in the Second Screen Community Group before being considered in the Working Group.

Remote Playback API

An API that allows a web application to request display of media content on a connected display, with a means to control the remote playback from the initiating page and other authorized pages.

Draft state: CR / Stable

Expected completion: Q4 2020 — The Working Group plans to publish the Remote Playback API as a final Recommendation when the Success Criteria are met.

Reference Draft: https://www.w3.org/TR/2017/CR-remote-playback-20171019/
Associated Call for Exclusion on 19 October 2017 ended on 18 December 2017
Produced under Working Group Charter: https://www.w3.org/2014/secondscreen/charter-2016.html

Additional features will be considered for the Remote Playback API to align it with the work on the Open Screen Protocol, based on implementation experience with that protocol.

Additional features will also be considered to improve compatibility with the Presentation API and remote playback of additional media types that are supported by the Open Screen Protocol.

All API changes will be incubated in the Second Screen Community Group before being considered in the Working Group.

Open Screen Protocol

A suite of network protocols that allow user agents to implement the Presentation API and the Remote Playback API in an interoperable fashion for browsers and presentation displays connected via the same local area network.

Draft state: Adopted from the Second Screen Community Group

Expected completion: Q2 2021

The Working Group may decide to group the API and protocol suite in one or more specifications.

Other Deliverables

Test suite

A comprehensive test suite for all features of a specification is necessary to assess the specification's robustness, consistency, and implementability, and to promote interoperability between user agents. Therefore, each specification must have a companion test suite, which should be completed before transition to Candidate Recommendation, and which must be completed with an implementation report before transition to Proposed Recommendation. Additional tests may be added to the test suite at any stage of the Recommendation track, and the maintenance of an implementation report is encouraged.

Additionally, this Working Group will improve test automation for the Presentation API and Remote Playback API test suites. This will be done through the adoption of a Testing API, incubated in an appropriate Community Group. The Testing API will also allow developers to use automation to test their own Web applications that make use of the above-mentioned APIs.

Use cases and requirements

The Working Group is strongly encouraging the participants to create and maintain a use cases and requirements document for each specification.

Implementation guidelines

To facilitate interoperability among user agents and display devices and encourage adoption of the API, the group may provide informative guidelines for implementors, either directly as informative notes within the Presentation API or in a separate non-normative group Note.

Other non-normative documents may be created for each specification, for example:

Primers
Non-normative schemas for language formats
Non-normative group notes

Milestones

Milestones
Specification	FPWD	CR	PR	Rec
Note: See changes from this initial schedule on the group home page.
Presentation API	-	-	Q4 2021	Q4 2021
Remote Playback API	-	-	Q4 2020	Q4 2020
Open Screen Protocol	Q1 2020	Q4 2020	Q2 2021	Q2 2021

Success Criteria

To advance to Proposed Recommendation, each specification is expected to have two independent implementations of each feature defined in the specification.

To advance to Proposed Recommendation, interoperability between the independent implementations should be demonstrated. Interoperable user agents hosting the same Presentation API web application should be able to render the same content with the same functionality on supported presentation displays that are compatible with the content to render.

The specifications produced by this Working Group will include security and privacy considerations. Specifically, the user must always be in control of privacy-sensitive information that may be conveyed through the APIs, such as the visibility or access to presentation displays, or the URLs of the web content to be presented. Specifications should also avoid unnecessary or severe increases to fingerprinting surface, especially for passive fingerprinting.

This Working Group will follow a test as you commit approach to specification development, for specifications in CR or above.

Dependencies and Liaisons

Dependencies

The initial drafts of the Presentation API and of the Open Screen Protocol were prepared by the Second Screen Community Group. Upon approval of the Working Group, the Community Group ceased its work on the Presentation API and the core Open Screen Protocol specifications. The Community Group may work on other related deliverables where it is not clear enough how to proceed for it to be a work item for a Working Group, including on extensions to the Open Screen Protocol. The Community Group is only one possible source for work under future Working Group charters, but can serve to do initial exploration for some future work items.

The specifications produced by this Working Group adhere to the web's origin-based security model.

Common web technologies that this Working Group could refer to for messaging include Web Messaging and the Web Socket API.

No external dependencies against the specifications of this Working Group have been identified.

Liaisons

For all specifications, this Working Group will seek horizontal review for accessibility, internationalization, performance, privacy, and security with the relevant Working and Interest Groups, and with the TAG. Invitation for review must be issued during each major standards-track document transition, including FPWD and at least 3 months before CR, and should be issued when major changes occur in a specification.

Additional technical coordination with the following Groups will be made, per the W3C Process Document:

Second Screen Community Group: This group developed the initial version of the Presentation API and of the Open Screen Protocol, and focuses on enabling interoperability among implementations of the second screen APIs, encouraging implementation of the the APIs by browser vendors and establishing complementary specifications for the APIs.
Accessible Platform Architectures (APA) Working Group: To help ensure deliverables support accessibility requirements, particularly with regard to interoperability with assistive technologies, and inclusion in the deliverable of guidance for implementing the group’s deliverables in ways that support accessibility requirements.
Media and Entertainment Interest Group: This group provides use cases and requirements for second screen scenarios and thus important input on the deliverables developed by the Second Screen Working Group.
Web Real-Time Communications Working Group: This group defines relevant or potentially relevant specifications for establishing peer-to-peer communication channels between web applications.

External Groups

While the Presentation API does not have a direct dependency on any given set of protocols, the following is a tentative list of external bodies the Working Group should collaborate with to develop the Open Screen Protocol and allow the Presentation API and Remote Playback API to be implemented on top of widely deployed attachment methods for connected displays:

IETF: The IETF develops network protocols that presentation displays may support, and that form the core of the Open Screen Protocol. The Second Screen Working Group will liaise with relevant groups at IETF to assure proper and secure application of IETF protocols within the Open Screen Protocol. These groups include Extensions for Scalable DNS Service Discovery, QUIC, Transport Layer Security (TLS), Crypto Forum Research Group, and Concise Binary Object Representation Maintenance and Extensions. The Second Screen Working Group will also liaise with IETF to assess whether parts of the Open Screen Protocol apply to broader scenarios than the ones envisioned for the APIs. Those parts may be developed further in the IETF.
Open Connectivity Foundation: The Open Connectivity Foundation develops home network protocols that presentation displays may support, including the UPnP suite of protocols.
Web Hypertext Application Technology Working Group (WHATWG): WHATWG develops the HTML specification that contains the definition of the HTMLMediaElement interface that the Remote Playback API specification extends; as well as the Web sockets and the cross-document messaging interfaces after which the communication channel of the Presentation API is modeled.
Wi-Fi Alliance: The Wi-Fi Alliance develops home network protocols that presentation displays may support.

Participation

To be successful, the Second Screen Working Group is expected to have 6 or more active participants for its duration, and to have the participation of industry leaders in fields relevant to the specifications it produces.

The Chairs and specification Editors are expected to contribute half a working day per week towards the Working Group. There is no minimum requirement for other Participants. This Working Group will also allocate the necessary resources for building Test Suites for each specification.

The group also welcomes non-Members to contribute technical submissions for consideration, with the agreement from each participant to Royalty-Free licensing of those submissions under the W3C Patent Policy.

Communication

Teleconferences will be conducted on an as-needed basis.

This group primarily conducts its technical work on GitHub. The public mailing list public-secondscreen@w3.org is used for calls for consensus. Administrative tasks may be conducted in Member-only communications.

Information about the group (deliverables, participants, face-to-face meetings, teleconferences, etc.) is available from the Second Screen Working Group home page.

Decision Policy

This group will seek to make decisions through consensus and due process, per the W3C Process Document (section 3.3). Typically, an editor or other participant makes an initial proposal, which is then refined in discussion with members of the group and other reviewers, and consensus emerges with little formal voting being required.

However, if a decision is necessary for timely progress, but consensus is not achieved after careful consideration of the range of views presented, the Chairs may call for a group vote, and record a decision along with any objections.

To afford asynchronous decisions and organizational deliberation, any resolution (including publication decisions) taken in a face-to-face meeting or teleconference will be considered provisional.

A call for consensus (CfC) will be issued for all resolutions (for example, via email and/or web-based survey), with a response period from one week to 10 working days, depending on the chair's evaluation of the group consensus on the issue.

If no objections are raised on the mailing list by the end of the response period, the resolution will be considered to have consensus as a resolution of the Working Group.

All decisions made by the group should be considered resolved unless and until new information becomes available, or unless reopened at the discretion of the Chairs or the Director.

This charter is written in accordance with the W3C Process Document (Section 3.4, Votes), and includes no voting procedures beyond what the Process Document requires.

Patent Policy

This Working Group operates under the W3C Patent Policy (Version of 5 February 2004 updated 1 August 2017). To promote the widest adoption of Web standards, W3C seeks to issue Recommendations that can be implemented, according to this policy, on a Royalty-Free basis.

For more information about disclosure obligations for this group, please see the W3C Patent Policy Implementation.

Licensing

This Working Group will use the W3C Software and Document license for all its deliverables.

About this Charter

This charter for the Second Screen Working Group has been created according to section 5.2 of the Process Document. In the event of a conflict between this document or the provisions of any charter and the W3C Process, the W3C Process shall take precedence.

Charter History

The following table lists details of all changes from the initial charter, per the W3C Process Document (section 5.2.3):

Charter Period	Start Date	End Date	Changes
Initial Charter	13 October 2014	31 October 2016	none
Rechartered	3 November 2016	31 October 2017	Group name adjusted to reflect practice Deliverables updated to reflect current status New Presentation API Level 2 deliverable mentioned On-going efforts on protocols in Second Screen Community Group noted Other adjustments: liaisons, licensing text
Extended	17 October 2017	31 December 2017	End date adjusted
Extended	1 December 2017	31 January 2018	End date adjusted
Rechartered	2 February 2018	11 December 2019	Completion dates updated to reflect current implementation plans, dependency on Open Screen Protocol noted Dropped second version of the Presentation API. Intent to re-include it later on after incubation and completion of current version noted Intent to work on testing APIs after incubation in a Community Group noted in Test suite section Dropped reference to the discontinued Network Service Discovery API which was developed by the Device and Sensors Working Group Updated boilerplate text using current charter template Added "test as you commit" approach Adjusted group names in liaisons section accordingly
Rechartered	11 December 2019	31 December 2021	Replaced the term "screen" by "presentation display" for consistency with the APIs Put presentation of parts of an HTML document in scope of the Working Group Put the standardization of a protocol suite for the APIs in scope of the Working Group Added the Open Screen Protocol deliverable accordingly Listed relevant IETF group for the Open Screen Protocol in the liaisons section A few editorial updates