An Adaptive Approach for Authoring Interactivity for Rich Multimedia Content

Marko PalviainenVTT Technical Research Centre of Finland

P.O. Box 1000 FIN 02044 Espoo e-mail: marko.palviainen@vtt.fi

Sam Dutton BBC R&D Prototyping

Henry Wood House 3-6 Langham Place London W1A 1AA

e-mail: sam.dutton@bbc.co.uk

Abstract—This paper describes an adaptive content authoring approach, the LIMO Authoring Tool to support the usage of the approach, and two examples in which an editor is adapted for presentation skeletons. The adapted editor aids the users as they create content to be attached to the presentation skeleton that specifies a ready-made baseline (e.g. skeleton, layout, and code libraries) for the presentation. The adapted editor does not just facilitate content creation but can also reduce errors and provide more robust, error free content.

Keywords; template-based content authoring; adaptable editor; adaptation; interactive television

I. INTRODUCTION

There are two kinds of editors for content authoring: the generic editors and specialized editors. The generic editors (e.g. text/XML editors) provide generic tools/views for content authoring but cannot provide as good usability as editors (e.g. a SMIL editor in [10]) that provide specialized tools/views to aid/automate authoring of a specific kind of content. Unfortunately, often it requires too much effort/resources to provide a specialized editor for content that does not follow existing standards or is based on the drafts of future standards.

One possibility to avoid this problem is to either adapt content into a form that can be edited with a specialized editor (see [9] and [21]) or then to extend an existing editor with tools/views that aid authoring of a specific kind of content. This paper presents a novel approach that is capable of adapting a generic editor to aid template-based creation of content. The approach follows the idea of the motherboard of a desktop computer that has a set of slots for extension cards. In the approach a presentation skeleton is: i) used as the “motherboard” of a presentation and ii) has a set of slots for the content that can be attached to the templates of the presentation skeleton. The slot modules adapt the editor for the slots of the presentation skeleton, aid the creation slot-specific content elements, and generate code for the slot elements. The authors can create a model for a presentation and then generate code from the model. The generated code and the files of the presentation skeleton will together form the content presentation.

The other novel point of the approach is the fact that it is capable of providing an adapted modeling language for content authoring. Multimedia modeling languages such as Hypertext Design Model [13], Synchronized Multimedia Integration Language (SMIL 3.0) [6], LimSee3 [10][16] and UML 2.0 based Multimedia Modeling Language (MML) [20] are based on assumption that there is a generic structure

(and a meta-model) for multimedia presentations. However, it is very challenging to provide a meta-model to support modeling of all kind of content. For example, interactive content such as games and advertisements require specialized modeling elements. In our approach the slot-specific meta-models extend the very limited core meta-model and by this way form an adapted modeling language for content that is attached to the presentation skeleton.

This paper makes two contributions: i) it presents the adaptive content authoring approach and ii) describes the LIMO Authoring Tool to support the use of the approach. After this introduction, Section II introduces background related to the approach. An overview of the approach, the LIMO Authoring Tool, and a demonstration for the use of the approach is given in Sections III and IV. Our findings and experiences are discussed in Section V. Conclusions are finally drawn in Section VI.

II. BACKGROUND The work presented in this paper relates to the P2P-Next

project (http://p2p-next.org/) that builds a reference next generation peer-to-peer (P2P) content delivery platform called NextShare, and approaches to aid professionals and consumers at home to create content to be delivered via the NextShare. The Lightweight Interactive Media Object (LIMO) framework aims at providing an interactive TV platform integrated with the NextShare, using the Web as a return channel from the viewer to the broadcaster. The rest of this section focuses on interactive TV standards, frameworks and authoring methods.

A. Standards Early research on digital TV has focused on the efficient

distribution of a digital content stream and the commercial packaging and protection of licensed TV content [8]. This work produced three regional body standards: Advanced Television Systems Committee (ATSC) standard in North America, International Standard for Digital Broadcasting (ISDB) in Japan and Brazil, and Digital Video Broadcasting (DVB) standard in Europe. These organizations have also considered ways to make the relatively passive TV environment more interactive [8].

The Multimedia Home Platform (MHP) is an open and interoperable specification for interactive TV [23]. The MHP is a part of the DVB standard and defines a generic interface that enables creation of interactive digital applications that can be executed in MHP terminals [15]. The MHP 1.1 platform can also deal with applications

2011 IEEE International Symposium on Multimedia

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DOI 10.1109/ISM.2011.39

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written in DVB-HTML, which is a combination of a subset of WWW standards (XHTML 1.1 modules, CSS2 etc.). The Interactive Broadcast and Internet Access profiles include support for the return channel in the MHP receiver.

The presentation engines of the three main Digital TV (DTV) systems — BML [5], DVB-HTML [19] and ACAP-X [4] — use an XHTML-based language [21]. Furthermore, the Brazilian DTV system, named Ginga uses the declarative Nested Context Language for creation of declarative and procedural applications [22].

B. Authoring of interactive multimedia presentations The existing authoring tools enable the authors to

specify the content, layout, and temporal flow of a multimedia presentation [20]. The What You See Is What You Get (WYSIWYG) paradigm used for static documents is not relevant for timed content: it is not possible to specify a dynamic behavior and immediately see its result [10]. Dedicated authoring, template-based authoring and reduced synchronization features aid authoring of timed multimedia presentations [10]. For example, the LazyMedia supports template-based video authoring [14]. Beside timelines, script languages and templates, intermediate approaches have been proposed through "direct manipulation" and multi-view interface paradigms [10]. The next approaches are used in the authoring tools [12]:

a) Timed-based metaphor – in which the multimedia elements are presented and organized in tracks along a time line. For example, Adobe Premiere [1] uses this metaphor.

b) Theatrical metaphor – in which media objects are the cast members on the stage and the score is a sequencer that animates the actors. For example, Adobe Director [2] uses this metaphor. Timed-based and theatrical metaphors are simple and intuitive, but are hard to manage and maintain, since a change to the time of an event can require adjustments to the time relationships between objects.

c) Flowchart-based paradigm – in which media objects are placed in a sequence and grouped into sub-routines, like commands in procedural programming. For example, Macromedia Authorware [3] uses the flowchart-based paradigm. With this metaphor the author cannot explicitly define the time intervals ruling the multimedia presentation, which are computed according to the execution order of the media components [12].

C. Authoring of LIMO presentations On-demand, personalized, and interactive television

requires a generic, non-proprietary, and lightweight solution to support live streaming, basic interactivity such as events, actions, and links, and the P2P architecture and other types of networks. The LIMO framework is designed for these requirements. It is extendable, is based on open standards, is free to use, and consist now of HTML5 [26] documents, Cascading Style Sheets [25] and JavaScript libraries. Web browsers and Internet-connected TV set-top-boxes and TVs can render a LIMO presentation that can contain:

a) LIMO assets – such as subtitles, chapters, texts, thumbnails images, HTML links and other media elements.

b) LIMO extensions – such as code libraries, game templates, and other interactivity code that add new functionalities to LIMO presentations.

c) Timings and event data – that represent the state data of a “receiver” Web page element for a particular range of values emitted by a “sender”. For example, the text displayed in a subtitle element is synchronized with the playback time of a video.

At least four kinds of stakeholders can participate in the authoring of LIMO presentations:

d) Content producers – produce video and audio contents for LIMO presentations.

e) Asset creators – insert new assets such as links, text, images to a presentation. In addition, advertisers may want to embed advertisements into the presentations.

f) Metadata creators – produce and attach metadata to presentations. For example, copyright and IPR managers may want to embed metadata to ensure that copyrighted material is correctly handled in a presentation.

g) LIMO extension / template developers – develop the LIMO framework, templates, and code libraries that enable new kinds of content to be used in the presentations.

The legacy tools aid the content authoring. Unfortunately, there was no tool for attaching content to the presentation skeletons. Thus a new approach was needed to aid professionals and consumers at home to create presentations that are based on various kinds of presentation skeletons and on the new versions of the LIMO framework.

We have previously developed the FEdXML [17] to provide a framework and ready-made components for XML editors. We decided to use the FEdXML as a starting point and to develop i) an XML editor and ii) an approach that adapts the editor to aid authoring of LIMO presentations.

III. AN ADAPTIVE APPROACH FOR TEMPLATE-BASED CONTENT AUTHORING

Our adaptive approach supports authoring of content that is attached to the templates of a selected presentation skeleton. The XML elements of the templates specify a unique identifier (URL) for each content slot, priorities for slots, and stakeholders who are assumed to edit the slot elements. The XML elements in various templates can relate to a single slot. Thus, a type is defined for the XML elements and used when the slot-specific content is attached to the templates.

Fig. 1 depicts the five main steps that relate to the approach:

a) The adaptation of the editor – will produce an adapted modelling language and adapted user interface for content authoring.

b) Project creation – A project folder and initial files are created for the presentation.

c) Modelling – The author uses the adapted editor and creates a model for the presentation.

d) Composition of a presentation – generates code from the model. The generated code and the files of the presentation skeleton will together form the presentation.

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e) Testing – checks that the presentation works as expected. If the presentation requires further development the process continues to the step c.

The next subsections describe these steps in more detail.

A. The adaptation of the editor The slot-specific meta-models extend the core meta-

model and by this way form an adapted modeling language (see Fig. 2) for the presentation skeleton. The language will have three kinds of elements:

a) The Presentation element – A container for the slot elements specifying a name for the presentation.

b) The Slot elements – Specifies name and stakeholders for the slot. It is a container for a single slot-specific element or for a sequence of slot-specific elements.

c) The Content elements – Fig. 2 depicts three slot-specific meta-models that enable modelling of a presentation that can contain a video and quizes.

The adaptation modules produce an adaptive user interface that can provide stakeholder specific tools/views for content authoring. The author can select a role from the list of the stakeholder names that are defined in the slot elements. The editor is now adapted for the role. For example, the slot elements/attributes that do not relate to the role can be hidden and elements that the stakeholder should edit can be emphasized in the user interface.

The code generation requires that the correct information is provided in the model. However, it is difficult for the author to know exactly what kind of information the model must provide. In order to avoid this problem and to improve the usability, the slot module does not just generate code for the slot elements but will also:

a) Create initial slot elements – that aids the authors to insert the required information to the slot elements of the model. For example, a slot module of a video slot can insert an empty video element to the model.

b) Reset slot elements – to the initial state. The slot module removes the child elements of the slot element, then inserts initial elements to the slot element, and thus facilitates the author to replace the content of a slot.

c) Validate slot elements – and guide the author to complete required information for the model. For example, a video slot module can guide the author to insert the missing video source element to the model.

B. Project creation This step produces a project folder and model for the

presentation. The author defines a name and project folder and selects a presentation skeleton for the presentation. The files of the presentation skeleton are then copied to the project folder. Subsequently, an initial model is automatically generated for the presentation skeleton: i) Slot elements are created first, attempting to find template factories for all the files of the presentation skeleton. Nothing is done if a template factory is not found for a file type. Otherwise a template factory is engaged to produce a template representation that provides an easy access to the slots that are defined in the template file.

Figure 1. An adaptive approach for template-based content authoring.

Figure 2. A core meta-model and three slot-specific meta-models.

The slots are sorted into correct order (by using their priority attribute) and slot elements are created and inserted into the Presentation element of the model. ii) The slot modules are then engaged to inset initial slot elements into the model.

C. Modelling The adapted editor provides two kinds of editing

controls for the model: i) Basic editing controls – that are based on the adapted modeling language and enable the author to add, remove, and edit the elements of the model. ii) Slot-specific authoring tools – that facilitate insertion of the slot-specific elements in the model.

For example, it is a laborious task to create subtitle elements for a video with standard editing controls. A slot module can provide an optional slot-specific tool that reads the subtitles from a SRT file, inserts corresponding subtitle elements to the model and thus greatly improves the creation of subtitles. The slot modules can also provide preview modules to display slot elements in the preview view. For example, a preview for the subtitles can further facilitate the authoring of the presentation.

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D. Composition of a presentation The composed presentation contains generated files and

the files of the project folder. The composition is performed in the next steps:

a) Removal of the previously generated files –The names of generated files start always with the “generated_” identifier. Thus it is easy to indentify and remove these files from the project folder.

b) Code generation – The slot modules will generate code for the slot elements to the slots and to the additional files (e.g. WebSRT files) of the presentation.

c) Files are written to the project folder – The slot-specific code is generated to the tagged sections of the templates or to the additional files. The XML elements describing the slots are then removed from the produced presentation files that are then stored to the project folder.

E. Testing The presentation can be tested at two levels: First, the

unit-level testing can test the slots separately. Second, the integration-level testing can ensure that the all parts of the presentation work properly. For example, the functionality testing of Web applications (e.g. LIMO presentations) requires typically tools for test model generation, code instrumentation, driver and stub generation, test result analysis, and report generation [11]. It is important to note that the created model can be utilized in testing, too. For example, the code generation step can produce code for functionality testing (e.g. code for instrumentation, drivers, stubs, test results analysis, and test report generation). However, this paper focuses on template-based content authoring and thus the testing issues are not in the focal point of the paper and are not discussed in more detail here.

IV. LIMO AUTHORING TOOL

The LIMO Authoring Tool is is a research prototype that support the usage of the adaptive authoring approach in the creation of LIMO presentations. It is implemented in Java and provides an XML editor and extension points for adaptation modules and is capable of creating a LIMO project, model, and presentation. Plug-in based systems have typically configuration files to describe the plug-ins used. The LIMO Authoring Tool does not need configuration files for plug-ins but uses the reflection feature of Java and automatically uses the adaptation modules that exist in the class path of the tool. The next paragraphs discuss the main parts of the tool:

The Project Creator creates a project folder, copies the files of the selected presentation skeleton to the project folder, and generates an initial model for the presentation.

The XML editor – provides an XML tree view, basic editing facilities for the XML elements, and a preview display for presentations. The editor enables the author to add and remove elements and to edit attributes of the elements of the model. In addition, copy, cut, and paste and undo and redo operations are provided for XML editing.

The Generator performs the composition of the presentation. It removes the previously generated files,

orchestrates code generation actions, and stores the produced presentation files to the project folder.

The next subsections present two examples in which the tool is adapted for presentation skeletons.

A. Example I – Adaptation for the Tree of Life presentation skeleton The BBC developed the Tree of Life presentation

prototype manually. The prototype uses the LIMO JavaScript library and the HTML5 video element for synchronising the content of Web page elements with the current time of a video. Subtitles, a carousel widget, and a panel displaying content from Wikipedia are updated in synchronisation with playback of the video. The video can be navigated by clicking on chapter thumbnails in a carousel widget; links to Wikipedia articles in the content panel display full articles as a page overlay. The prototype also demonstrates how page elements can be rendered over the HTML video element. The jQuery library, jCarousel and ThickBox are used in the prototype. The timed LIMO data used in the prototype was hardcoded within index.html in object literal format. The presentation was used as a starting point for the Tree of Life presentation skeleton. Firstly, we created a folder for the skeleton, then copied the files and folders of the Tree of Life presentation to the folder, and finally removed the content that is not needed in the skeleton (e.g. the Tree of Life-specific video and images) from the folder. Then, we replaced the hardcoded timed LIMO data with XML elements describing slots for video, chapters, and subtitles, and finally zipped the presentation skeleton files to a zip file. Subsequently, we implemented the next adaptation modules for the presentation skeleton:

a) HTML Template Factory – Composes a template representation for an HTML file.

b) Video Module – provides a meta-model and an initializer, validator, code generator, and preview for the video elements. The code generator adds an HTML video element to the slot of the HTML template. The provided slot-specific tool aids the user to attach a video file to the model and the preview displays the video file for the user.

c) Chapters Module – provides a meta-model and an initializer, validator, code generator, and preview for chapter elements.

d) Subtitles Module – provides a meta-model and an initializer, validator, code generator, and preview for subtitle elements. A slot-specific tool is provided to import subtitles from a SRT file to the model and to export the subtitle elements in an SRT format from the model.

The adaptation modules will now aid the authoring of video, chapter, and subtitle elements for presentations that are based on the Tree of Life presentation skeleton.

B. Example II – Adaptation for the extended version of the Tree of Life presentation skeleton The Tree of Life presentation skeleton uses JavaScript

code for chapter and subtitle rendering. In order to support usage of more versatile chapter and subtitle content in presentations, we decided to extend the presentation skeleton to both support usage of WebSRT mark-up in the

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However, although there are many benefits in the approach, the next issues may limit its utilization:

a) It must be possible to use an adapted meta-model in the editor – It is required that there is a model editor that is capable of utilising the adapted meta-model.

b) Extension points are needed for adaptation modules – The number of the extension points of the editor can set limitations for the adaptation. Thus a specialized editor can be a better than an adapted editor because it can provide a fully tailored user interface. However, often it requires too much effort to create a specialized editor for the authoring of a specific kind of content. In this case the adapted editors can aid/automate content authoring, reduce errors and provide more robust, error free content.

VI. CONCLUSIONS

This paper describes an adaptive content authoring approach and the LIMO Authoring Tool to aid the usage of the approach in the creation of LIMO presentations. The approach produces an adapted modelling language and adaptive user interface to aid/automate the authoring of content that is attached to a presentation skeleton. The slot modules create initial elements for a slot, reset slot elements, validate slot elements, generate code from the slot elements and can optionally provide specialised tools and previews for slot elements, too. The slot modules are now provided for video, subtitle, chapter and WebSRT slots.

ACKNOWLEDGMENT

The research leading to these results has received funding from the 7th Framework Programme (FP7/2007-2013) under grant agreement No. 216217 (P2P-Next).

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