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 3 November 2016
End date 31 December 2017
Confidentiality Proceedings are Public
Initial Chairs Anssi Kostiainen
Initial Team Contacts
(FTE %: 20)
François Daoust
Usual 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:

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.

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: Q2 2017

Presentation API Level 2

A second version of the Presentation API that integrates features which the Working Group resolved not to include in the first version in the interest of time, feedback from Web developers on the first version, as well as stable features matured in the Second Screen Community Group, provided they fall within the scope of this Working Group. The Working Group's issue tracker lists examples of features that may be integrated.

Draft state: No draft (builds on the CR) / Exploring

Expected completion: Progress on this specification depends on the adoption of the first version of the Presentation API and on the outcomes of discussions within the companion Second Screen Community Group. This Working Group does not expect to complete this specification by the end of this charter and may request to be re-chartered to finalize this work, possibly with a different scope.

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: FPWD / Refining

Expected completion: Q3 2017

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 a implementation report is encouraged.
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 - - Q2 2017 Q2 2017
Presentation API Level 2 Q3 2017 - - -
Remote Playback API - Q2 2017 Q3 2017 Q4 2017

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 will cease its work on the Presentation API specification. It is expected that the Community Group will recharter to 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.

Even though the scopes of the APIs are different, some of the use cases that the Presentation API aims to address, in particular projection of web content on second screens connected to the local area network, are also in scope of the Network Service Discovery API worked upon by the Device and Sensors Working Group. This Working Group will liaise with the Device and Sensors Working Group, in particular to help ensure consistency of supported service discovery mechanisms when a user agent implements both APIs.

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

Liaisons

The Working Group expects to maintain contacts with at least the following groups and Activities within W3C (in alphabetical order) and ask for wide reviews of its deliverables before publication as Candidate Recommendation, and where appropriate:

Device and Sensors Working Group
The Device and Sensors Working Group defines the Network Service Discovery API that addresses some of the use cases that are in scope of the Second Screen Working Group.
HTML Media Extensions Working Group
The Second Screen Working Group may interact with the HTML Media Extensions Working Group on the interaction between media extensions and the Remote Playback API specification.
Privacy Interest Group
The Second Screen Working Group intends to secure reviews on its deliverables from the Privacy Interest Group to help ensure they offer the right level of protection to users.
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 will specify a set of network protocols that 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.
Web and TV 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.
Web Security Interest Group
The Second Screen Working Group intends to secure reviews on its deliverables from the Web Security Interest Group to help ensure they offer the right level of security.

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:

DLNA
The Digital Living Network Alliance references home network protocols that secondary displays may support.
IETF
The IETF develops home network protocols that secondary displays may support.
UPnP Forum
The UPnP Forum develops home network protocols that secondary displays may support.
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 10 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

As explained in the W3C Process Document (section 3.3), this group will seek to make decisions when there is consensus and with due process. The expectation is that 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 should put a question out for voting within the group (allowing for remote asynchronous participation -- using, for example, email and/or web-based survey techniques) and record a decision, along with any objections. The matter should then be considered resolved unless and until new information becomes available.

Any resolution taken in a face-to-face meeting or teleconference is to be considered provisional until 10 working days after the publication of the resolution in draft minutes sent to the working groups mailing list. If no objections are raised on the mailing list within that time, the resolution will be considered to have consensus as a resolution of the Working Group.

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

Patent Policy

This Working Group operates under the W3C Patent Policy (5 February 2004 Version). 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