Wendy Van den Broeck

Assessing Quality of Experience of IPTV and Video on Demand Services in Real-Life Environments

The ever growing bandwidth in access networks, in combination with IPTV and video on demand (VoD) offerings, opens up unlimited possibilities to the users. The operators can no longer compete solely on the number of channels or content and increasingly make high definition channels and quality of experience (QoE) a service differentiator. Currently, the most reliable way of assessing and measuring QoE is conducting subjective experiments, where human observers evaluate a series of short video sequences, using one of the international standardized subjective quality assessment methodologies. Unfortunately, since these subjective experiments need to be conducted in controlled environments and pose limitations on the sequences and overall experiment duration they cannot be used for real-life QoE assessment of IPTV and VoD services. In this article, we propose a novel subjective quality assessment methodology based on full-length movies. Our methodology enables audiovisual quality assessment in the same environments and under the same conditions users typically watch television. Using our new methodology we conducted subjective experiments and compared the outcome with the results from a subjective test conducted using a standardized method. Our findings indicate significant differences in terms of impairment visibility and tolerance and highlight the importance of real-life QoE assessment.

Seeing the bigger picture: a user perspective on 360° TV

Omnidirectional video (ODV) is a type of video in which viewers can look around in 360° as if turning the camera themselves. This type of video presents opportunities for new interactive television formats. The development of such new formats, however, is accompanied by challenges in terms of user experience and technical and creative development. In this paper, we discuss which issues and opportunities users anticipate. These findings are the result of a human-centered design study in which we first introduced potential users to ODV, gathering their feedback, and then encouraged them to envision suitable ODV-based enhancements of television genres.

Speckle disturbance limit in laser-based cinema projection systems.

In a multi-disciplinary effort, we investigate the level of speckle that can be tolerated in a laser cinema projector based on a quality of experience experiment with movie clips shown to a test audience in a real-life movie theatre setting. We identify a speckle disturbance threshold by statistically analyzing the observers’ responses for different values of the amount of speckle, which was monitored using a well-defined speckle measurement method. The analysis shows that the speckle perception of a human observer is not only dependent on the objectively measured amount of speckle, but it is also strongly influenced by the image content. The speckle disturbance limit for movies turns out to be substantially larger than that for still images, and hence is easier to attain.

Integrating the everyday-life context in subjective video quality experiments

Controlled subjective quality experiments are a well-known method to make decisions on the improvement of Quality of Service (QoS) of video streams. Recently it became clear that from a point of view of the consumer or user, the Quality of Experience (QoE) is more relevant and can influence the optimal QoS as determined in a lab-setting. The measurement of QoS parameters in a lab-setting does not take into account the specific context of the practice that is under examination (e,g. watching video content). In this paper we discuss a method of contextualized subjective quality experiments as we applied in different research projects in complement to the standardized lab-experiments. The strength of this method is that video and audio quality is assessed in the real-life context of the user, i.e. his or her natural habitat in which the behavior or practice normally takes place. We provide an overview of how we applied the contextualized research approach in two cases. Next we discuss the methods strengths and weaknesses and suggest a refinement of the methodology.

The promises of iDTV: between push marketing and consumer needs

In this paper, we discuss the push and pull dynamics of the introduction of interactive digital television and the discrepancy between promised and actual practices as lived by the audience. Our analysis is based on a case study of iDTV in Flanders in which we analysed both the promises as can be found in the political economical rhetoric about iDTV and the lived appropriation practices of viewers with their motives to switch or not to switch to interactive digital television.

Assessing the importance of audio/video synchronization for simultaneous translation of video sequences

Lip synchronization is considered a key parameter during interactive communication. In the case of video conferencing and television broadcasting, the differential delay between audio and video should remain below certain thresholds, as recommended by several standardization bodies. However, further research has also shown that these thresholds can be relaxed, depending on the targeted application and use case. In this article, we investigate the influence of lip sync on the ability to perform real-time language interpretation during video conferencing. Furthermore, we are also interested in determining proper lip sync visibility thresholds applicable to this use case. Therefore, we conducted a subjective experiment using expert interpreters, which were required to perform a simultaneous translation, and non-experts. Our results show that significant differences are obtained when conducting subjective experiments with expert interpreters. As interpreters are primarily focused on performing the simultaneous translation, lip sync detectability thresholds are higher compared with existing recommended thresholds. As such, primary focus and the targeted application and use case are important factors to be considered when selecting proper lip sync acceptability thresholds.

OMUS: an optimized multimedia service for the home environment

Media content in home environments is often scattered across multiple devices in the home network. As both the available multimedia devices in the home (e.g., smartphones, tablets, laptops, game consoles, etc.) and the available content (video and audio) is increasing, interconnecting desired content with available devices is becoming harder and home users are experiencing difficulties in selecting interesting content for their current context. In this paper, we start with an analysis of the home environment by means of a user study. Information handling problems are identified and requirements for a home information system formulated. To meet these requirements we propose the OMUS home information system which includes an optimized content aggregation framework, a hybrid group-based contextual recommender system, and an overall web-based user interface making both content and recommendations available for all devices across the home network. For the group recommendations we introduced distinct weights for each user and showed that by varying the weights, the coverage (i.e., items that can be returned by the recommender) considerably increases. Also the addition of genre filter functionality was proven to further boost the coverage. The OMUS system was evaluated by means of focus groups and by qualitative and quantitative performance assessment of individual parts of the system. The modularity of internal components and limited imposed hardware requirements implies flexibility as to how the OMUS system can be deployed (ranging from e.g., embedded in hardware devices or more software services based).

From Era of Plenty to Era of Overflow What Shall I Watch

This article focuses on how viewers decide what to watch in a context of almost infinite video content availability and a lasting expansion of the process of digitization. We investigate to what extent viewers apply an active search process toward video content. Therefore we applied a focus group methodology. Seven focus group sessions were conducted, totaling 47 participants. We found that this process is guided by a combination of contextual, content-related, and personal factors, which simultaneously free as well as restrict the viewer in his choice. Moreover it can be concluded that a gradual shift is taking place in who fulfills the gatekeeper’s role.

Developing a Multi-Device Immersive TV-Experience: User Expectations and Practices

This paper discusses the results of a closed lab pilot test featuring a documentary on a football school in Porto. The documentary was displayed as regular directed TV-content on an HD TV-screen and participants could use a Samsung Gear VR HMD and a tablet to watch it in 360°. 27 participants participated in the test and testing took place with individual viewers and in teams of 2. The aim of the lab test was to investigate how people would make use of this multi-device set-up (which devices do they use, length of the interaction, do they stand or sit down) and whether they consider this a social experience. Also, the influence of the 360° experience on the storyline was questioned. Each session was observed and afterwards an interview took place to discuss the experience. Respondents were rather enthusiastic about this experience. Even though the HMD tends to isolate people, it was still considered a social experience and people talked about the content and the experience. A main limitation of the set-up was the difference in audiovisual quality between the content on TV and the content on the VR and the tablet, which was not in HD.

Extending the field of view: a human-centred design perspective on 360° TV

Omnidirectional video (ODV) is a type of video that presents viewers with a new type of interactivity. It enables people to look around in a 360° view of the recorded dynamic scene as if they are controlling the camera themselves. ODV presents opportunities for new interactive television formats. The development of such new formats, however, is accompanied by challenges in terms of user experience and technical and creative development. In this article, we discuss issues and opportunities tied to televising ODV from a user perspective. These findings are the result of a human-centred design study. In this study, we introduced 20 potential users to ODV, as this was new to them. We gathered their feedback on the demonstration, and then encouraged them to envision suitable ODV-based enhancements of television genres. This article offers a discussion of both the methodology (including a form of laddering) applied in the study and the user research findings. We found that people see an added value in ODV under certain conditions (e.g. enabling exploration), but that there are also a number of bottlenecks such as the concern to miss key parts of a television programme while looking around.