W3C

Second Screen Working Group Charter

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

Join the Second Screen Working Group

Start date 2 February 2018
End date 31 December 2019
Charter extension See Change History
Chairs Anssi Kostiainen
Team Contacts François Daoust (0.2 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, particularly editors, regularly use the #webscreens W3C IRC channel

Goals

Web content is available on an ever expanding array of devices including ebook readers, phones, tablets, laptops, auto displays, and electronic billboards. These devices have a variety of display screens. There are also a variety of mechanisms that allow these devices to use secondary display screens 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 wirelessly through Miracast, WiDi, or AirPlay. Wireless screens may be available on a local area network or over the Internet, brokered by a cloud service. A device like a laptop could provide a screen for a smaller device like a phone.

For many of these techniques the operating system hides how the screen is attached and provides ways for native applications to use the screens. Native applications on an operating system can easily use these additional screens without having to know how they are attached to the device. At this point, however, there is no way for a web page to take advantage of these available secondary displays.

The Second Screen Working Group aims at defining simple APIs that allow web applications to show and control web content on one or more secondary displays.

Scope

The scope of this Working Group is to define 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. Pages may become authorized to control the web content by virtue of sharing an origin with the originating page, explicit user permission, or other facilities provided by the user agent. The API will hide the details of the underlying connection technologies and use familiar, common web technologies for messaging between the authorized pages and the web content shown on the secondary display. The web content may comprise HTML documents, web media types such as images, audio, video, or application-specific media, depending on the capabilities of the secondary display for rendering the media. Application-specific media includes that whose type is known to the controlling page and the connected display, but not necessarily a generic HTML user agent.

The API will provide a means to identify whether requesting display on second screens is likely to be successful, i.e. whether at least one secondary screen is available for display.

The API is agnostic with regard to the display connection used, and also works with display connections that support video only, for example, a TV connected to a laptop with an HDMI connection. In such a usage scenario, the web content displayed on a connected display must be rendered and converted to video before it is sent to a second screen. The user agent may use whatever means the operating system provides to prepare and send the video to a second screen. Any interaction between the authorized web pages and the content displayed on a secondary screen would happen within the bounds of the initiating device since both the pages and the content are rendered on that same device, and only a video representation is sent to the second screen.

Alternatively, if the second screen device understands some other means of transmitting content to a display and a means of two-way message passing, the web content can be rendered by the remote device. In this scenario, a URL to the content to be displayed is sent to the secondary display to be rendered there. Because the content is rendered separately from the initiating user agent, pages hosted by other user agents may be authorized to control the remotely rendered content at the same time.

For a requested piece of web content, how and by which device the content is rendered is an implementation detail. The user agent is responsible for determining which secondary displays are compatible with the content that is requested to be shown through the API.

Sending content to a connected display creates a presentation session. Applications can create multiple presentation sessions to control multiple displays, although synchronization between them is not currently supported by the API.

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 secondary displays.

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

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 secondary displays that are compatible with the content to render.

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:

This Working Group will not define or mandate network protocols for sharing content between user agents and secondary displays. For example, the following are out of scope:

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

To facilitate interoperability among user agents and display devices and encourage adoption of the API, the group may informatively reference existing suites of protocols, either directly in the Presentation API deliverable or in a non-normative companion Note. This Working Group will monitor the outcomes of related discussions in the Second Screen Community Group in particular.

Content mirroring, whereby a web application requests display of the content shown in its own browsing context (i.e., page) on a secondary display, is out of scope. If a web application requests display of itself (same URL) on a connected display, a new browsing context will be created with that URL and rendered on the connected display.

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.

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

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 2019 — 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.

The Open Screen Protocol, under incubation in the Second Screen Community Group, 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.

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 2018 — This Working Group does not anticipate further changes to this specification. The Working Group plans to publish the Remote Playback API as a final Recommendation when the Success Criteria are met.

The Working Group may decide to group the API functions 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:

Milestones

Milestones
Note: See changes from this initial schedule on the group home page.
Specification FPWD CR PR Rec
Presentation API - - Q4 2019 Q4 2019
Remote Playback API - - Q4 2018 Q4 2018

Dependencies and Liaisons

Dependencies

The initial draft of the Presentation API was prepared by the Second Screen Community Group. Upon approval of the Working Group, the Community Group ceased its work on the Presentation API specification. The Community Group is currently focused on incubating the Open Screen Protocol, an open set of network protocols that includes authentication and security mechanisms, for the APIs defined in this Working Group. The Community Group may also 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. 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 security model defined in the HTML specification published by the Web Platform Working Group.

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

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 focuses on enabling interoperability among implementations of the Presentation API, encouraging implementation of the Presentation API by browser vendors and establishing complementary specifications for the Presentation API. The Community Group incubates the Open Screen Protocol for the APIs defined in this Working Group. This work on protocols may warrant changes in the Presentation API.
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 Platform Working Group
The Web Platform Working Group’s deliverables cover the security model implemented in Web Browsers; as well as other relevant specifications such as Web IDL, HTML5 Web Messaging, The Web Socket API and the HTML specification that contain the definition of the HTMLMediaElement interface that the Remote Playback API specification extends.
Web Real-Time Communications Working Group
This group defines relevant or potentially relevant specifications for establishing peer-to-peer communication channels and for extending the Presentation API to support out-of-scope features such as content mirroring.

External Groups

The Presentation API does not have strong dependencies on any given set of protocols. The following is a tentative list of external bodies the Working Group should collaborate with to allow the Presentation API to be implemented on top of widely deployed attachment methods for connected displays:

IETF
The IETF develops home network protocols that secondary displays may support.
Open Connectivity Foundation
The Open Connectivity Foundation develops home network protocols that secondary displays may support, including the UPnP suite of protocols.
Wi-Fi Alliance
The Wi-Fi Alliance develops home network protocols that secondary 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 work on the public mailing list public-secondscreen@w3.org. 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 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 31 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