The contrast effect: QoE of mixed video-qualities at the same time

In desktop multi-party video-conferencing videostreams of participants are delivered in different qualities, but we know little about how such composition of the screen affects the quality of experience. Do the different videostreams serve as indirect quality references and the perceived video quality is thus dependent on other streams in the same session? How is the relation between the perceived qualities of each stream and the perceived quality of the overall session? To answer these questions we conducted a crowdsourcing study, in which we gathered over 5000 perceived quality ratings of overall sessions and individual streams. Our results show a contrast effect: high quality streams are rated better when more low quality streams are co-present, and vice versa. In turn, the quality p

Perceptual quality of 4K-resolution video content compared to HD

With the introduction of 4K UHD video and display resolution, questions arise on the perceptual differences between 4K UHD and upsampled HD video content. In this paper, a striped pair comparison has been performed on a diverse set of 4K UHD video sources. The goal was to subjectively assess the perceived sharpness of 4K UHD and downscaled/upscaled HD video. A striped pair comparison has been applied in order to make the test as straightforward as possible for a non-expert participant population. Under these conditions and over this set of sequences, on average, on 54.8% of the sequences (17 out of 31), 4K UHD resolution content could be identified as being sharper compared to its HD down and upsampled alternative. The probabilities in which 4K UHD could be differentiated from downscaled/upscaled HD range from 83.3% for the easiest to assess sequence down to 39.7% for the most difficult sequence. Although significance tests demonstrate there is a positive sharpness difference from camera quality 4K UHD content compared to the HD downscaled/upscaled variations, it is very content dependent and all circumstances have been chosen in favor of the 4K UHD representation. The results of this test can contribute to the research process of developing metrics indicating visibility of high resolution features within specific content

Group Modeling : selecting a sequence of television items to suit a group of viewers

Peer reviewedPostprin

Quality of experience for adaptive streaming using HTTP Dynamic Streaming

This thesis investigates how to establish the relationship between OSI layer 7 parameters of video streaming and the QoE of the user, and to evaluate which methods are most tting for the estimation of QoE. The project is made in cooperation with LTH and Acreo, and is a part of the Next generation over-the-top multimedia services (NOTTS) 7and the Eco system for Future Media Distribution (EFRAIM) project. The underlying techniques, which form the environment of our research of estimating the QoE, is adaptive bitrate streaming over TCP. The purpose is to investigate how a service, that provides a user with the means to benchmark the received quality of the Over the top (OTT) streaming service, can be built and distributed. Today there exists no such service that takes the viewers subjective opinion into consideration. There have been extensive research on some connected elds and issues but none with a unied solution to streaming adaptive bitrate video over TCP with its particular behavior and eect caused on the streamed video. In this report we evaluated two dierent methods of prediction of QoE, Pause Intensity based on the number of pauses and their length during playback, and a Linear bitrate model based on the average bitrate quality and its standard deviation. We also made a small user test with our streaming client software to evaluate the two methods to decide which one is the most benecial to use. The test showed that although one of the most irritating playback deficiencies is when pauses occur, the linear bitrate model delivered the most accurate predictions

The quality of experience of emerging display technologies

As new display technologies emerge and become part of everyday life, the understanding of the visual experience they provide becomes more relevant. The cognition of perception is the most vital component of visual experience; however, it is not the only cognition that contributes to the complex overall experience of the end-user. Expectations can create significant cognitive bias that may even override what the user genuinely perceives. Even if a visualization technology is somewhat novel, expectations can be fuelled by prior experiences gained from using similar displays and, more importantly, even a single word or an acronym may induce serious preconceptions, especially if such word suggests excellence in quality. In this interdisciplinary Ph.D. thesis, the effect of minimal, one-word labels on the Quality of Experience (QoE) is investigated in a series of subjective tests. In the studies carried out on an ultra-high-definition (UHD) display, UHD video contents were directly compared to their HD counterparts, with and without labels explicitly informing the test participants about the resolution of each stimulus. The experiments on High Dynamic Range (HDR) visualization addressed the effect of the word “premium” on the quality aspects of HDR video, and also how this may affect the perceived duration of stalling events. In order to support the findings, additional tests were carried out comparing the stalling detection thresholds of HDR video with conventional Low Dynamic Range (LDR) video. The third emerging technology addressed by this thesis is light field visualization. Due to its novel nature and the lack of comprehensive, exhaustive research on the QoE of light field displays and content parameters at the time of this thesis, instead of investigating the labeling effect, four phases of subjective studies were performed on light field QoE. The first phases started with fundamental research, and the experiments progressed towards the concept and evaluation of the dynamic adaptive streaming of light field video, introduced in the final phase

Ergonomics of the Operative Field in Paediatric Minimal Access Surgery

Imperial Users onl

Development of a Quality of Service Framework for Multimedia Streaming Applications

By the year 2012, it is expected that the majority of all Internet traffic will be video content. Coupled with this is the increasing availability of Wireless Local Area Networks (WLANs) due to their ease of deployment, flexibility and reducing roll out costs. Unfortunately the contention based access mechanism utilised by IEEE 802.11 WLANs does not suit the non-uniform or bursty bandwidth profile of a video stream which can lead to a reduced quality of service (QoS) being experienced by the end-user. In 2005, the IEEE 802.11e protocol was ratified in an attempt to solve this emerging problem. It provides for an access prioritization mechanism based upon four separate traffic classes or access categories (ACs). Each AC is characterised by a set of access parameters that determine its level of access priority which is turn determines the amount of bandwidth available to it. Computer simulation studies have shown that AC prioritisation can yield significant improvements in the QoS delivered over a WLAN. However, these studies have been based upon the use of static access parameters for the ACs. In practice, this is not a viable solution owing to the dynamic and unpredictable nature of the operating conditions on WLANs. In this thesis, an experimental study of AC prioritisation based upon adaptive tuning of the access parameters is presented. This new approach to bandwidth provisioning for video streaming is shown to yield significant improvements in the QoS under a wide range of different operating conditions. For example, it is shown that by adaptively tuning the access control parameters in response to the network conditions, the number of video frames delivered that satisfy QoS requirements is more than doubled