The Virtual Video Gallery: a user-centred media on-demand ...si.deis.unical.it/~fortino/research/publications/journal/...will play a strategic role in the context of distance learning

The Virtual Video Gallery: a user-centred

media on-demand system

1. INTRODUCTION

The convergence of multimedia, virtual reality andthe Internet is promoting the development oflarge-scale, interactive Multimedia VirtualEnvironments (MVEs) (Ferscha & Johnson 1999)characterized by easy accessibility, which integratemultimedia streaming into a virtual world.Application domains ranging from education toentertainment, from health care to military simula-tions, can be supported and made more appealingby exploiting MVEs. In particular, MVEs enhanceuser experience, which is no longer bound to staticGUIs but depends on audio, video and virtual real-ity objects, and favour usability by means of intu-itive features, metaphors of the real world, such asspeech, vision and gestures.

A low-cost development of MVEs over the

Internet can be effectively supported by integrat-ing the following key enabling technologies: (i) theWEB (World Wide Web Consortium 2003), whichprovides a robust client/server infrastructure whichcan be ubiquitously accessed; (ii) Java (JavaTechnology 2003), which is currently the mostemployed platform and language for developinglarge-scale distributed applications; (iii) VRML(Virtual Reality Manipulation Language) (Carey1998), which allows for both the easy constructionand the standard representation of complex virtualworlds.

In particular, these MVEs can be exploited topromote the use of Internet-based Media on-Demand (MoD) systems (Fortino et al. 2002b) thatwill play a strategic role in the context of distancelearning and recreation by providing access anddelivery of archived multimedia objects. In fact,

Interactive Technology & Smart Education (2004) 1: 29–40© 2004 Troubador Publishing Ltd.

Giancarlo Fortino and Wilma Russo

Dipartimento di Elettronica, Informatica e Sistemistica (DEIS), Università della Calabria, Via P. Bucci cubo 41C, Rende (CS), 87036, Italy

Email: {g.fortino, w.russo}@unical.it

The convergence of multimedia, virtual reality and the Internet is promoting low-cost multimedia virtual environmentswhich are easily accessible to large network communities. These environments, which facilitate usability and enhanceuser experience, are very suitable for supporting user-oriented application domains such as e-learning and entertain-ment. This paper presents a multimedia virtual environment, namely the Virtual Video Gallery, an advanced, distrib-uted media on-demand system which is browsable through a virtual world. By taking a virtual walk inside the gallery,the user can interactively select, preview, watch and control multimedia sessions. While the user-centred design of thesystem relies on UML-based modelling techniques, system implementation is obtained by the integration of Java,VRML and Web-based technologies. In order to evaluate the user-oriented effectiveness of the Virtual Video Galleryand compare it to currently available Internet-based MoD systems, the usability testing of the system was establishedfor deriving both summative and formative usability data.

Keywords Multimedia virtual environment, Media on-demand, Java, WWW, VRML, usability testing

VOL 1 NO 1 FEBRUARY 2004 29

the MoD systems, which are currently available onthe Internet, are still not fully exploited. This isdue to (i) general issues affecting all distributedmultimedia applications which offer audio/videostreaming and (ii) issues which specifically addressthe MoD systems. Among the latter, the human-computer interface has a relevant role in that itsusability and degree of appeal can strongly influ-ence the intensive use of a MoD system.

This paper presents an original Internet-basedmultimedia virtual on-demand environment – theVirtual Video Gallery (VVG) – that can be appliedfor both entertainment and education. The VVG isobtained through the modular composition of adistributed MoD system and a virtual world. Bynavigating the virtual world which reproduces anart gallery where media objects are exhibited, theuser can choose and query a media object, and, ifinterested, can start and control the audio/videopresentation which is associated with the selectedmedia object. In particular, the VVG architectureis composed of:

• the Gallery Server, which is the web-based serv-ice access point;

• the Media Servers, which provide streaming ofarchived multimedia presentations;

• the Virtual Client, which contains the videogallery virtual world and the media presenter,which are separate components interactingthrough a standard interface.

The implementation of the VVG is currently basedon key enabling technologies, so obtaining easyaccessibility of the system through a web browserand multi-platform portability for both the serverand the client.

Since the main design goal of the VVG is to pro-vide a user-centred MoD system which is appeal-ing, easy-to-use and particularly productive for thefinal user, usability testing of the VVG is being car-ried out to obtain both summative and formativeusability data (Hilbert and Redmiles 2000). Thefinal aim of the usability testing is to evaluate theeffectiveness of integrating a virtual reality worldwith an Internet-based MoD system and to derivegeneral practises for designing and developing user-centred MoD systems. The evaluation of severalavailable Internet-based MoD systems and theircomparison with the VVG is thus also being car-ried out. Preliminary analysis indicates that theVVG may overcome the main issues which preventthe MoD systems currently available on theInternet from being widely and intensively used.

The rest of this paper is structured as follows. In

section 2 the most exploited key enabling tech-nologies are overviewed and their integration forbuilding Internet-based MVEs is discussed.Section 3 details the design goals and the architec-ture of the VVG. Section 4 describes the modellingand some snapshots of the virtual multimedia GUIof the VVG. Section 5 overviews some representa-tive commercial and research-oriented Internet-based MoD systems. Section 6 discusses usabilityissues of Internet-based MoD systems and illus-trates the usability testing which is being carriedout. Finally, in Section 7, conclusions are drawn anddirections of future work delineated.

2. INTEGRATING MULTIMEDIA AND VIRTUAL REALITY TECHNOLOGIES ON THE INTERNET

Advances in communications, computers and soft-ware are transforming the Internet from a meta-network to a world-wide computing platformwhich is able to provide a large set of diversifiedservices. The World Wide Web (WWW) has facil-itated such a transformation by providing an appli-cation-level infrastructure atop of the Internetwhich allows users to access resources and servicesaccording to the client/server paradigm. In the lastfew years notable research efforts have been devot-ed to developing interactive multimedia applica-tions and virtual worlds using the WWW as thebasic infrastructure in order to reach as much audi-ence as possible. The most recent deliverables,which have already become widely used de factostandards, encompass IP-based multimedia stream-ing technology (Crowcroft et al. 1999; McCanne1999) and the Virtual Reality ManipulationLanguage (VRML) along with its related tools.

An issue which is still open, however, is how toeffectively integrate the available Internet-basedmultimedia technologies with virtual reality(Brutzman 1998; Mueller and Neuhold 1998).

The Java platform allows for the realization of aneffective solution based on:

• the Java Media Framework (JMF) (Java MediaFramework 2000), which is an API providingextensive support for the development ofInternet-based multimedia applications. In par-ticular, it includes media encoders/decoders (e.g.MPEG 1 and 4), media players, and mediastreaming and control protocols such as theRealtime Transport Protocol (RTP) (Shulzrinneet al. 1996) and the Real Time Streaming

Fortino and Russo: The Virtual Video Gallery

INTERACTIVE TECHNOLOGY & SMART EDUCATION30


Protocol (RTSP) (Schulzrinne et al. 1998), whichare Internet Request For Comments (RFCs).

• the External Authoring Interface (EAI) (EAI1997), which is a standard interface enabling theinteraction between a virtual world defined byVRML and a Java applet in the context of a webbrowser. In particular, the interaction is based onboth out-events, which can be captured from thevirtual world and elaborated by the Java applet,and on in-events, which are sent from the Javaapplet to the virtual world to change its globalstate. The implementation of EAI is differentaccording to which VRML player (e.g., Cosmoplayer (Cosmo Software 2000) or Cortona player(Cortona 2003)) is used. Currently, two versionsexist: version 1.0, implemented by Netscape, andversion 2.0, implemented by Cortona.

Figure 1 portrays a two-tier reference architecturalschema upon which a specific Java-based multime-dia virtual environment can be built.

The web server archives the VRML file of thevirtual world, the code of the JMF-based applet,the HTML entry page which contains tags toembed both the VRML file and the Java applet,and the classes related to JMF and EAI.

MVE activation and execution is supported by aJava-compliant web browser enhanced with aVRML player plug-in. Visually, the MVE showsitself as two aligned windows: one based on the“look and feel” of the VRML player which displaysthe virtual world, and the other based on the GUIof the JMF-based Applet.

The JMF-based applet is served by a media server

which provides streaming of media objects ondemand according to a specific application logic. Themedia streaming transport protocol can be based onRTP and the streaming control protocol on RTSPeven though proprietary protocols can be exploited.

The proposed schema provides a weak integra-tion in that the audio/video objects are handled inthe Java applet and are not embedded in the virtu-al world. A complete merging requires the ad-hocimplementation of a multimedia virtual playerwhich can introduce heavy performance issues onthe client side in the context of a massively hetero-geneous environment like the Internet. A proto-type is reported in (de Oliveira et al. 2003), which isbased on Java 3D API and JMF.

3. THE VIRTUAL VIDEO GALLERY

The main goal of the Virtual Video Gallery (VVG)system is to create a multimedia virtual environ-ment (MVE) on the Internet for browsing andstreaming archived multimedia sessions. In partic-ular, the VVG design goals are as follows:

• Web-based service access point. Using the web as themain gate to the VVG services makes the VVGeasily and world-wide accessible by means of aweb browser.

• Dynamic client installation. Users do not have toinstall any additional software; the software theyneed for connecting to the VVG is dynamicallyinstalled on-demand under the form of a Javaapplet.

• Browsing supported by a dynamic virtual world. Adynamic virtual world (Brutzman 1998) resultingfrom the integration of a VRML-based virtualworld and Java enhances the plain navigabilityfeatures of hypertexts and improves the userexperience with respect to a traditional “click-based” GUI.

• Distributed MoD server. Although the access tothe services of the VVG is centralized so to pro-vide the user with a single point of contact, themedia streaming architecture of the server(transparently to the user) is fully distributed.

• Highly-interactive playback. The playback of thearchived multimedia sessions is based on thestandard Internet protocols for media streamingand control.

• Multi-platform portability. By relying on the Javaplatform, Web technologies, VRML and theInternet multimedia protocol stack, the systemis endowed with an intrinsic multi-platformportability.


Figure 1 A reference architectural schema for Java enabledintegration of multimedia streaming and virtual reality on

the WWW

• Improved usability with respect to existing Internet-based MoD systems. Usability is a key issue influ-encing the adoption of existing Internet-basedMoD systems; merging the multimedia GUI withVirtual Reality is expected to improve usability.

3.1 The system architecture

The architecture (Figure 2) of the VVG system,which was designed (Fortino et al. 2002a) using theUnified Modelling Language (UML) and its multi-media extensions (Baumeister et al 1999; Sauer andEngels 2001), is an improvement upon the referencearchitectural schema proposed in section 2. Theserver side is organized like a Content DistributionNetwork (CDN) to which clients can connect andask for services. In particular, the VVG consists ofthe following three main components: the GalleryServer, the Media Server, and the Virtual Client.

The Gallery Server (GS) is the VVG service accesspoint and is composed of:

• a Web Server, which allows for the download ofboth the HTML entry page of the VVG and theHTML page in which the application client isembedded;

• the Gallery Application Server (GAS), which isa Java remote-enabled, thread-safe object sup-ported by the RMI Naming Server (or RMI reg-istry), provides the following functionalities: (i)authentication of the users through a login andpassword; (ii) access to and retrieval of themovie list and information; (iii) admission con-trol for the incoming client requests. Theadmission control policy is based on the avail-ability of the requested movie and on the actualload of the system.

• relational databases which archive the list of theregistered users and information about theavailable movies.

The Media Server (MS) is the network entity whichprovides movie posters, trailers and streaming ofmovies. MSs can dynamically join (or register to)and leave (or deregister from) a chosen GS thuscontributing to create loosely coupled media clus-ters. The MS is composed of:

• the Web Server, which is intended for HTTP-based remote retrieval of images (files in GIFformat) and trailers (small-sized MPEG files).

• the Movie Repository, which contains RTP-based media files, obtained using the ViCROsystem (Fortino and Nigro 2003) by dumpingRTP-based sessions, which were generated byRTP-based audio/video conference tools(McCanne 1999).

• the Media Streamer (MStr), which is a multime-dia networked component, re-used and adaptedfrom the ViCRO system, which reads RTP-based media files and streams them back ontothe network. MStr can be interactively con-trolled by means of its RTSP-based interface.

• the Movie Application Server (MAS), which is aremote-enabled, thread-safe object supported bythe RMI Registry and performs the followingtasks:

– submission and update of the local movie list and information to the GS;

– activation and control of an MStr; – calculation of system load parameters to

accept or refuse requests for streaming movies.

The MAS interacts with a relational databasewhich contains information about the availablelocal movies.

The Virtual Client (VC) allows a user to connect tothe GS, navigate the VVG, and select a movie. Itconsists of:

• the Java Media Applet (JMA), which enables auser to perform the following tasks: authenticat-ed log-in, movie searching, visualization of infor-mation about movies, preview of trailers andpresentation and control of movie playbacks. Inparticular, the presentation of multimedia objectsis based on the Java Media Framework (JMF)library (Java Media Framework 2000). While awhole movie is streamed, a movie trailer trans-mission is based on an HTTP bulk transfer.



Figure 2 Architectural schema of the VVG.


• the VRML-based World (VW), which representsan art gallery dislocated on several circular floorswhich are linked by an elevator. Each floor con-tains movie posters organized by genre (e.g.thriller, comics, fantasy, horror, drama, comedy,action). By walking through the Gallery, a usercan select a movie by simply clicking on its poster.After the selection, information about the movieare displayed on the JMA GUI. The VW wasmodelled using 3D Studio MAX R3 (3D StudioMax R3 1999), a professional computer graphicstool, which is able to export the modelled virtualworld into a VRML file (wrl). This file was suc-cessively enhanced with manually-insertedVRML code to allow for timed animations (e.g.movement of the environmental cameras, move-ment of the elevator among floors, etc.) andtouch-sensible areas (e.g. the movie poster panels,the elevator buttons, etc.). The adopted VRMLplayers are the Cosmo Player (Cosmo Software2000) and the Cortona Player (Cortona 2003).

The VW and the JMA interact with one anotherthrough the External Authoring Interface (EAI). Inparticular, when specific VRML events (e.g. causedby user navigation) occur in the VW, the JMA isfirst notified about the event type by the EAI inter-face and then it carries out the corresponding eventhandling. For instance, when a user in the virtualgallery clicks on the movie poster, the generation ofan event occurs; such an event is captured by theJMA which translates it to a movie informationrequest at the GS. The JMA can also send eventsinto the VW that can affect either the behaviour orthe structure of the VW itself. For instance, when anew movie is available, its poster is automaticallyexposed in the Gallery by sending a specific eventwhich changes the Gallery structure.

The interactions between the GS and the MS,and between the VC and the GS depend on the JavaRMI middleware (Java Technology 2003). In partic-ular, the GAS and the MAS continuously interact toperform content management. The media and con-trol flows exchanged during the playback stagebetween the VC and the MStr are based on theReal-time Transport Protocol (RTP) (Shulzrinne etal. 1996) and the Real Time Streaming Protocol(RTSP) (Shulzrinne et al. 1998), respectively.

4. THE MULTIMEDIA VIRTUAL GUI

4.1 The modelling

To model the static presentation and the dynamic

timed behaviour of the multimedia virtual GUI,graphical elements and concepts were borrowedfrom UML-based multimedia languages and pur-posely integrated. In particular, the navigationalmodel and the static presentational model ofHyper-UML (Baumeister et al. 1999) and the multi-media model-view-controller model (MVCMM) ofOMMMA-L (Object-oriented MultiMediaModelling Application Language) (Sauer andEngels 2001) were used. The basic concepts ofthese models can be summarised as follows:

• The navigational model formalizes the naviga-tion structure of the hypermedia applicationsusing a class diagram which specifies nodes andobject diagrams (context, primitives, structure)and shows how these nodes are visited. The stat-ic presentational model offers a collection ofuser interface objects (UML composite objects)through which a GUI is modelled.

• The MVCMM is an extended Model-View-Controller model which incorporates: a classdiagram (Modelstatic) consisting of a hierarchy ofmedia-type definitions and the logical applica-tion model; an extended sequence diagram(Modeldynamic) describing temporal behavioursuch as inter- and intra-media synchronization;a presentation diagram showing the spatial lay-out (View) of a GUI; a statechart (Controller)specifying spontaneous behaviour caused byuser interactions or other system events.

In particular, the presentation diagram of theMVCMM was constructed by using the compositeobjects of the Hyper-UML static presentationalmodel. This improves the expressiveness of thestatic GUI specification.

According to this approach, a multimedia appli-cation can be modelled by specifying: (i) the logicalstructure (classes and associations); (ii) media types(live captured and stored in a DB); (iii) temporalbehaviour (synchronization); (iv) spatial arrange-ment and presentation (audio, video, GUI); (v)interactive and event-driven dynamics. Figure 3visualizes the integrated specification diagram ofthe multimedia virtual GUI. The logical structure(MSTAT section) of the multimedia Virtual GUIincludes the association of application objects tomedia types, i.e. the static part of the model aspectof MVCMM. The multimedia Virtual GUI (orMMVAppl) is an aggregation of a VWorld (theVirtual World) and a MMAppl. The latter is com-posed of one or more MMApplUnit which can con-sist of one or more multimedia composite compo-nents. The temporal diagram (MDYN section)


shows the synchronization between the video andthe audio tracks of a movie. The “C” sectionreports a simplified statechart of the interactivemultimedia virtual GUI controller. The statecharthas two main concurrent states which representthe behaviour of the JMA and that of the VirtualWorld. In particular, the VIRTUALWORLD state issplit into two further concurrent states in whichthe surfing of the Virtual World and someautonomous animations are performed. Externalevents, i.e. sent from the JMA, are always listenedto. The “V” section portrays an excerpt of the stat-ic presentation specification. It consists of the log-ical view of the main GUI of the JMA, along withthe Movie Info, the Movie Search and the MoviePlay GUI.

4.2 The user interaction

The entry page of the VVG allows for: (i) theinstallation of the Virtual Client according to thefollowing modes: “with the virtual world” or “with-out the virtual world”; (ii) the registration of a useras a VVG user.

A registered user can follow the “Enter withVRML World” link so that the complete VVGClient is downloaded. Before the activation of theVVG, the user has to log into the VVG by means ofthe log-in dialog of the JMA. Once activated, theVVG Client GUI appears as shown in Figure 4,where the virtual world is on the right and theApplet GUI appears on the left. The numbered

items were introduced on the snapshot to highlightkey elements of the Multimedia Virtual GUI.

By default, a user starts surfing the Gallery fromthe first floor, which contains the Action movies. Amovie can be selected in the following manner:

• the user can move by means of the VRML play-er, directly in front of the movie poster area (seeitem 1), and click on its touch-sensitive area;

• the user can employ the GUI of the JMA toselect a movie from the floor movie list (seeitem 3).

To browse movies of another genre the user caneither change floor using the elevator (see item 2) orsearch for movies of specific genres by using thesearching GUI (Figure 5a) of the JMA which isenabled by the SEARCH button (see item 8). Aftera movie has been selected, it is possible to list itsinformation (Figure 5b), display its poster, previewits trailer, and start the whole movie presentation bymeans of the buttons labelled by the items 4, 6, 5, 7,respectively. The whole movie is presented on awindow which is undocked from the JMA as shownin Figure 6.

5. RELATED INTERNET-BASED MOD SYSTEMS

In the following the basic characteristics of thecommercial and research-oriented MoD systems,which are being used in the usability testing (seesection 6), are briefly described.

5.1. Research prototypes

5.1.1 ViCROThe Video Conference Recording On-demand sys-tem (ViCRO; Fortino and Nigro 2003), developed



Figure 3 The Virtual GUI integrated specification

Figure 4 The main window of the Multimedia Virtual GUI


at University of Calabria, is a multicast-based VoDsystem over MBone and WWW which allows forrecording, playback and browsing of archived mul-timedia sessions. The server side of the system iscompletely implemented in Java whereas the clientside is partially Java-enabled. The GUI of theclient consists of two parts: the Java AWT-basedcontrol GUI and the media GUI which consists ofthe MBone tools (vic and vat). ViCRO is stronglybased on the following Internet standard proto-cols: RTP/RTCP for media streaming, RTSP forstreaming control and SDP for media sessiondescription.

5.1.2 JMFVoDThe Java Media Framework Video on Demand sys-tem (JMFVoD; Belda et al. 2002), developed atPolitechnique of Valencia, is a Java-based VoD sys-tem which consists of a stand-alone VoD server

application, a web-integrated VoD client, and adatabase which contains all the available multi-media files in MPEG format. While the mediastream transport layer is based on RTP/RTCP, thestreaming control is proprietary and provides simi-lar functionality of RTSP.

5.1.3 KOMSSYSThe KOM(S) streaming system (Komssys; Zink etal. 2001), developed at Technical University ofDarmstadt, is a VoD platform for experimentalresearch. It is implemented in C++ using a compo-nent-based approach and provides a server, a client,and a proxy cache for MPEG-based audio/videostreaming. As ViCRO, Komssys is based onRTP/RTCP, RTSP and SDP. The client GUI hasbeen built using the Qt graphical toolkit.

5.2. Commercial systems

5.2.1 Real NetworksThe Real Networks streaming technology (RealOne 2003; Helix Universal Server 2003), developedby Real Networks, allows for the construction ofweb-based media streaming on-demand systems,which are based on the Real One media player atthe client side and on the Helix Universal Server atthe server side. The Real One media player pro-vides playback of audio and video streaming as wellas web-based browsing of media objects. The HelixUniversal Server provides support for streaming allmajor media types, including RealAudio/RealVideo, Apple’s QuickTime, MPEG-4 andWindows Media.

5.2.2. Windows MediaThe Windows Media technology (Windows MediaServer 2003; Windows Media Player 2003), devel-oped by Microsoft, enables the development ofInternet-based MoD systems by providing theWindows Media Player, the Windows Media


Figure 5 The (a) Searching and (b) Information GUIs of the JMA

Figure 6 The media streaming and control GUI

Server, and encoding tools. The Windows MediaPlayer allows a user to request the streaming of aremote media file on-demand and to play its con-tent. Streaming services are delivered through theWindows Media Server. Media file formats as wellas protocols for media streaming and streamingcontrol are proprietary.

5.2.3 DarwinThe Darwin Streaming system (Darwin 2003),developed by Apple, is an open source version ofApple’s QuickTime Streaming Server technologythat allows for the transmission of streaming mediato clients across the Internet using the industrystandard RTP and RTSP protocols. The client isrepresented by the Apple QuickTime, which canplay MPEG 4 and QuickTime-based media streams,whereas the server is the Darwin Streaming Serverv5.0.

6. USABILITY EVALUATION

6.1 Basic concepts

Usability evaluation can be defined as the act ofmeasuring or identifying potential issues affectingusability attributes of a system or device withrespect to particular users, while performing partic-ular tasks, and in particular contexts (Hilbert andRedmiles 2000). Usability attributes can varydepending on the background knowledge and expe-rience of users, the tasks for which the system isused, and the context in which it is used. Usability,which is the issue of how satisfactorily users canmake use of the system functionality, is traditional-ly associated with the following attributes (Nielsen1993):

(i) Learnability: the system should be easy to learnso that the user can rapidly accomplish tasksusing the system. Learnability problems maylead to increased training, staffing, and usersupport or corrective maintenance costs.Learnability is often associated to memorabil-ity, i.e. the system should be easy to remember,so that the casual user is able to return to thesystem after a period of time, without repeat-ing the learning process.

(ii) Performance efficiency and effectiveness: in termsof speed and error, the system should be effec-tive and efficient to use, so that once the userhas learned the system, a high level of produc-tivity is possible.

(iii) Flexibility: the system should support the use

of different commands and strategies toachieve the same task.

(iv) Error Tolerance and System Integrity: the systemshould have a low error rate, so that usersmake few errors during the use of the system,and when made, can easily recover from them.Further, unrecoverable errors must not occur.

(v) User Satisfaction: the system should be aesthet-ically pleasant and enjoyable to use, so thatusers are subjectively satisfied when using it

From the usability evaluation, it is thus possibleto obtain usability data which can be used to deter-mine the utility as well as the usability of the sys-tem. It is worth noting that the aforementionedusability attributes, also referred as dimensions ofusability testing (or evaluation), characterize allsoftware systems interfacing final users. In particu-lar, multimedia applications introduce new andpeculiar usability issues (Lee 1999; Petersen 1998)which are further amplified if multimedia applica-tions distributed over the Internet are considered.Thus, although theory and methods developed tosupport usability evaluation of traditional applica-tions are not specific to deal with the usability eval-uation of multimedia applications, they can beemployed once purposely tuned.

6.2 Usability issues in MoD systems on the Internet

The usability of Internet-based media on-demand(MoD) systems is affected by both general issues(Synnes et al. 2001) which are common to all the dis-tributed multimedia applications on the Internetproviding transmission and reception of audio/videostreams, and by issues specific of MoD systems. Inparticular, the general issues are related to:

• the network quality, which can heavily affect thetransmitted media streams and also increasemessage latency. Without sufficient networkresources (e.g. bandwidth) it is difficult to suc-cessfully transmit and/or correctly receive mediastreams. Even using a low rate media stream, forinstance composed of a 128 Kbps video streambased on H.263 and 13 Kbps audio stream basedon GSM, a bandwidth of at least 141 Kbps isneeded, which is greater than the maximumbandwidth furnished by an ISDN line (128Kbps). In fact, although video frame losses canbe masked and more easily tolerate by users, lossrates of more than 2% can make the audio tire-some to listen to. So it is important to have the




necessary quality of service in terms of band-width and loss rate from the network, eventhough techniques for repairing and/or forintroducing redundancy at the source can beexploited to alleviate the problem. In addition,due to frequent packet losses the interactivity ofmessaging between users or of controlling aremote resource can be limited.

• the desktop hardware and software environment,which concur to diminish the audio/video quali-ty at the client. PC-based media playing toolssuffer from the problem that audio hardware ispractically hard to set-up without risking echofeedback or noise. This is the main cause whynon-expert people find difficulty when usingthese environments. Moreover, the video qualityused in low-bandwidth configurations (typicallymaximum 128 Kbps of video) is oftentimes con-sidered “awful” and “jerky”. People are used tocomparing the perceived video quality to that ofTV with the consequence being that there isoften a loss of interest. The audio quality suffersfrom the same comparison. The only way toovercome this problem is to increase the per-ceived quality by sending more data or by using amore effective encoding. Another important fac-tor to consider is the synchronization betweenthe lips of the speaker and the emitted speech(lip synchronization), which when un-synchro-nized disturbs the viewer of an audio/video pres-entation.

The specific issues, which were identified byanalysing the available commercial and research-oriented Internet-based MoD systems overviewedin section 5, are:

• Service unavailability, which limits users toaccess and exploit the service. In particular,from the user perspective the unavailability ofthe service is considered the most unpleasantevent since users are unable to use the system.

• Media object unavailability, which can limit usersfrom obtaining the requested media object.After selecting a media object on the basis ofhis/her preferences, a user expects to handle therequested media object, e.g. by controlling itsplayback. The denial of the requested mediaobject generates user dissatisfaction.

• Scarce interactivity of the control, which could notallow users to efficiently control the playback ofa media object. When a user sends a controlcommand, he/she wants to receive immediatefeedback and long waiting times annoy usersthat compare the interaction delays with the

high degree of interactivity of home VCRs.• Media object searching, which can obstacle users

from finding desired media objects. Usersshould be provided with a powerful and easy-to-use searching tool to search for media objectswhich fulfil the users’ needs.

• Multimedia graphical user interface, which can pre-vent the system from being extensively used.From the user perspective, the GUI is the visi-ble part of the system so, in the context of theInternet, it should be not only user-friendly andintuitive but also appealing since Internet usersare initially attracted more by the appearance ofan application (e.g. web site or applet) than itsusefulness per se.

The first three specific issues mainly depend onthe performances at the server side of a MoD sys-tem and on the network connecting users to the sys-tem. In particular, media streaming servers shouldbe dimensioned to serve the target audiencedepending on its expected size. Such dimensioningrequires an estimation of the maximum load thatthe system can sustain to guarantee availability ofservices and media objects as well as satisfactorydegree of control interactivity. The solutionemployed by our VVG system, as well as by themajority of similar systems, is to use a local clusterof media streaming servers or a widely-distributedCDN (Content Distribution Network). Under thehypothesis that the issues related to the server sideof the system and to the network have no influenceat all, users can always access, choose and interac-tively control any media objects they desire obtain-ing the requested Quality of Service (QoS). In thiscase, the remaining key issues are the functionalityof media object searching and, particularly, the mul-timedia GUI influenced by the desktop hardwareand software environment.

6.3 Usability testing of the VVG

Usability testing of the VVG aims at fulfilling thefollowing objectives:

• Making judgements about the VVG per se andcomparing competing systems (summative eval-uation).

• Acquiring feedback to inform and evaluatedesign decisions for reverse engineering of thesystem (formative evaluation).

• Understanding which potential the integrationof a virtual world and a classical multimediaGUI possesses to make an Internet-based MoD


system more “usable” (summative and formativeevaluation).

To this purpose, a general procedure of usabilitytesting (Rubin 1994) was customized and organizedin sequential steps as follows:

1. Planning a usability testEach user will be involved in a joint experimen-tation of the VVG and the “competing”Internet-based MoD systems cited in section 5.The profile of the user is that of a person whohas at least a practical information technologybackground (e.g. experience of advanced webbrowsing and knowledge of office automationtools). The employed usability testing method ispluralistic walkthroughs, even though empiricalmethods are also considered for very skilledpractitioners. The list of tasks a user has to per-form are: (i) testing the Internet-based MoDsystems mentioned in section 5 and filling a gen-eral questionnaire about each system; (ii) testingthe VVG system and filling its specific ques-tionnaire; (iii) filling a comparison questionnairewhich report the perceived differences betweenthe MoD systems and the VVG. Interviews arealso used after a test completion for collectingfurther data. The experimentation testbed (ortest environment) consists of a high-perform-ance PC-cluster (also open to Internet) based onthe Windows operating system. Inside such anenvironment, usability of the system is notaffected by issues such as network quality, serv-ice unavailability, media object unavailabilityand scarce degree of control interactivity.Moreover, the desktop hardware and softwareenvironment issues were also mitigated by appo-site settings. The media archive of the VVG iscomposed of RTP-based high-quality and low-quality movies. High-quality movies, which aredelivered to users inside the cluster (or internalusers), have the following characteristics: videorate c.a. 1 Mbps, video format CIF (CommonImage Format – 352 × 288 pixel), video encodingMPEG-1, audio encoding PCM u-law. Low-qual-ity movies, which are intended to serve usersoutside the cluster (external users), have the fol-lowing characteristics: video rate about 100Kbps, video format QCIF (Quarter CIF – 176 ×144 pixel), video encoding H.261, audio encod-ing GSM. Using such settings audio/video quali-ty is on average considered to be good for inter-nal users and acceptable for external ones. Testscan be carried out using both high-quality andlow-quality movies.

2. Selecting a representative sample and recruiting par-ticipantsAs the results of usability testing would be morevalid if the participants were typical end-user ofthe VVG, the chosen sample of participants is agroup of university students who had already butonly attended introductory computer sciencecourses, and thus similar to average users ofInternet.

3. Preparing the test materials and actual test environ-mentApart from activating the VVG system and theother MoD systems so making them ready to beused, additional materials such as task scenarios,prerequisite training materials (e.g. simplifieduser manuals), post-test questionnaires, anddebriefing guides are available before starting atest.

4. Conducting the usability testA typical test consists of at most two partici-pants supported by a passive test monitor whowas not expected to intervene in any way

5. Debriefing the participantAfter a participant completes to fill the ques-tionnaire, he/she is questioned to provide fur-ther information about the test.

6. Analysing the data of the usability testObtained data are inserted into an appositelydesigned data warehouse and analysed usingboth traditional statistical methods andadvanced data mining techniques.

7. Reporting the resultsThis is the last phase of the test in which thefinal report summarizing results, findings andrecommendations is produced.

To date a limited usability testing of the VVGhas been carried out. Based on the obtained usabil-ity data, the preliminary results indicates that theVVG has a higher degree of usability than theother systems. In particular, the main information,that is emerging from the on-going evaluation, isthat using the assistance of the virtual world forbrowsing the movie archive makes the VVG themost appealing MoD system for medium and low-skilled users. Conversely more advanced users findthe Multimedia Virtual GUI too simple and lack-ing in customisation mechanisms but theynonetheless find this GUI more appealing than theclassical GUI of the other examined MoD systems.

7. CONCLUSIONS

Nowadays the Internet can actually support an



efficient deployment and exploitation of distrib-uted multimedia systems and applications. In par-ticular, interactive media on-demand systems areemerging since they can be effectively employed tosupport prominent application domains such as e-learning and entertainment. This paper has pre-sented the Virtual Video Gallery (VVG), anadvanced media on-demand system whose brows-ing functionalities are facilitated and enriched by avirtual world. Currently the VVG is specialized toserve the entertainment domain exhibiting moviesin the virtual world. Nevertheless, as the virtualworld is dynamically extendible and the Java applettransparently replaceable, the VVG can be easilycustomized for the education domain. To the bestof the authors’ knowledge, the VVG represents afirst serious attempt to integrate a virtual worldinto an Internet-based MoD system. Usability test-ing is therefore being conducted not only to evalu-ate the usability of the VVG for summative orformative purposes but also to gain insights intohow virtual reality and multimedia can be integrat-ed into the context of Internet-based MoD sys-tems. Preliminary tests show that using an effectivevirtual world to navigate the media archive can sig-nificantly augment the exploitation of Internet-based MoD systems which are, to date, under-used.Due to recent technological advances, furtherefforts will be devoted to improving the VVG. Inparticular, the VVG will be “restyled” using newmultimedia formats (e.g. MPEG-4), the RMI mid-dleware will be partially replaced with WebServices, and system security will be reinforcedusing media streaming encryption.

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Giancarlo Fortino is an Assistant Professor of Computer Science in the Department of Electronics, Informatics and Systems at theUniversity of Calabria, Cosenza, Italy. His research interests include distributed computing, Internet computing, multimedia systems,object- and agent-oriented technology. Fortino received a PhD in computer engineering from the University of Calabria. He is a mem-ber of the IEEE Computer Society and the ACM.

Wilma Russo is an Associate Professor of Computer Science at the Department of Electronics, Informatics and Systems of theUniversity of Calabria, Cosenza, Italy. Her research interests include parallel and distributed computing and systems, agent-orientedsystems, object-oriented technology, Internet computing.

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