On the impact of video stalling and video quality in the case of camera switching during adaptive streaming of sports content

The widespread usage of second screens, in combination with mobile video streaming technologies like HTTP Adaptive Streaming (HAS), enable new means for taking end-users' Quality of Experience (QoE) to the next level. For sports events, these technological evolutions can, for example, enhance the overall engagement of remote fans or give them more control over the content. In this paper, we consider the case of adaptively streaming multi-camera sports content to tablet devices, enabling the end-user to dynamically switch cameras. Our goal is to subjectively evaluate the trade-off between video stalling duration (as a result of requesting another camera feed) and initial video quality of the new feed. Our results show that short video stallings do not significantly influence overall quality ratings, that quality perception is highly influenced by the video quality at the moment of camera switching and that large quality fluctuations should be avoided

Incidence and duration of severe wasting in two African populations

Abstract Objective The present study aimed to compare two situations of endemic malnutrition among <5-year-old African children and to estimate the incidence, the duration and the case fatality of severe wasting episodes. Design Secondary analysis of longitudinal studies, conducted several years ago, which allowed incidence and duration to be calculated from transition rates. The first site was Niakhar in Senegal, an area under demographic surveillance, where we followed a cohort of children in 1983-5. The second site was Bwamanda in the Democratic Republic of Congo, where we followed a cohort of children in 1989-92. Both studies enrolled about 5000 children, who were followed by routine visits and systematic anthropometric assessment, every 6 months in the first case and every 3 months in the second case. Results Niakhar had less stunting, more wasting and higher death rates than Bwamanda. Differences in cause-specific mortality included more diarrhoeal diseases, more marasmus, but less malaria and severe anaemia in Niakhar. Severe wasting had a higher incidence, a higher prevalence and a more marked age profile in Niakhar. However, despite the differences, the estimated mean durations of episodes of severe wasting, calculated by multi-state life table, were similar in the two studies (7·5 months). Noteworthy were the differences in the prevalence and incidence of severe wasting depending on the anthropometric indicator (weight-for-height Z-score ≤-3.0 or mid upper-arm circumference <110 mm) and the reference system (National Center for Health Statistics 1977, Centers for Disease Control and Prevention 2000 or Multicentre Growth Reference Study 2006). Conclusions Severe wasting appeared as one of the leading cause of death among under-fives: it had a high incidence (about 2 % per child-semester), long duration of episodes and high case fatality rates (6 to 12 %

Subjective quality assessment of longer duration video sequences delivered over HTTP adaptive streaming to tablet devices

HTTP adaptive streaming facilitates video streaming to mobile devices connected through heterogeneous networks without the need for a dedicated streaming infrastructure. By splitting different encoded versions of the same video into small segments, clients can continuously decide which segments to download based on available network resources and device characteristics. These encoded versions can, for example, differ in terms of bitrate and spatial or temporal resolution. However, as a result of dynamically selecting video segments, perceived video quality can fluctuate during playback which will impact end-users' quality of experience. Subjective studies have already been conducted to assess the influence of video delivery using HTTP Adaptive Streaming to mobile devices. Nevertheless, existing studies are limited to the evaluation of short video sequences in controlled environments. Research has already shown that video duration and assessment environment influence quality perception. Therefore, in this article, we go beyond the traditional ways for subjective quality evaluation by conducting novel experiments on tablet devices in more ecologically valid testing environments using longer duration video sequences. As such, we want to mimic realistic viewing behavior as much as possible. Our results show that both video content and the range of quality switches significantly influence end-users' rating behavior. In general, quality level switches are only perceived in high motion sequences or in case switching occurs between high and low quality video segments. Moreover, we also found that video stallings should be avoided during playback at all times

Data Cleaning: Detecting, Diagnosing, and Editing Data Abnormalities

In this policy forum the authors argue that data cleaning is an essential part of the research process, and should be incorporated into study design