No abstract

Interactive branched video that allows users to select their own paths through the video, provides creative content designers with great personalization opportunities; however, such video also introduces significant new challenges for the system developer. For example, without careful prefetching and buffer management, the use of multiple alternative playback paths can easily result in playback interruptions. In this paper, we present a full implementation of an interactive branched video player using HTTP-based Adaptive Streaming (HAS) that provides seamless playback even when the users defer their branch path choices to the last possible moment. Our design includes optimized prefetching policies that we derive under a simple optimization framework, effective buffer management of prefetched data, and the use of parallel TCP connections to achieve efficient buffer workahead. Through performance evaluation under a wide range of scenarios, we show that our optimized policies can effectively prefetch data of carefully selected qualities along multiple alternative paths such as to ensure seamless playback, offering users a pleasant viewing experience without playback interruptions.

Abstract-In contrast to traditional video, multi-view video streaming allows viewers to interactively switch among multiple perspectives provided by different cameras. One approach to achieving such a service is to encode the video from all of the cameras into a single stream, but this has the disadvantage that only a portion of the received video data will be used, namely that required for the selected view at each point in time. In this paper we introduce the concept of a "multi-video stream bundle" that consists of multiple parallel video streams that are synchronized in time, each providing the video from a different camera capturing the same event or movie. For delivery we leverage the adaptive features and time-based chunking of HTTPbased Adaptive Streaming (HAS), but now employing adaptation in both content and rate. Users are able to change their viewpoint on-demand and the client player adapts the rate at which data is retrieved from each stream based on the user's current view, the probabilities of switching to other views, and the user's current bandwidth conditions. A crucial component of such a system is the prefetching policy. For this we present an optimization model as well as a simpler heuristic that can balance the playback quality and the probability of playback interruptions. After analytically and numerically characterizing the optimal solution, we present a prototype implementation and sample results. Our prefetching and buffer management solution is shown to provide close to seamless playback switching when there is sufficient bandwidth to prefetch the parallel streams.

Abstract-HTTP-based Adaptive Streaming (HAS) has become a widely-used video delivery technology. Use of HTTP enables relatively easy firewall/NAT traversal and content caching. While caching is an important aspect of HAS, there is not much public research on the performance impact proxies and their policies have on HAS. In this paper we build an experimental framework using open source Squid proxies and the most recent Open Source Media Framework (OSMF). A range of contentaware policies can be implemented in the proxies and tested, while the player software can be instrumented to measure performance as seen at the client. Using this framework, the paper makes three main contributions. First, we present a scenariobased performance evaluation of the latest version of the OSMF player. Second, we quantify the benefits using different proxyassisted solutions, including basic best effort policies and more advanced content quality aware prefetching policies. Finally, we present and evaluate a cooperative framework in which clients and proxies share information to improve performance. In general, the bottleneck location and network conditions play central roles in which policy choices are most advantageous, as they significantly impact the relative performance differences between policy classes. We conclude that careful design and policy selection is important when trying to enhance HAS performance using proxy assistance.

Background and Objectives: Chronic kidney disease (CKD) and spinal cord injury and disorders (SCI/D) are common and costly conditions among Veterans. However, little is known about CKD among adults with SCI/D. Methods: We conducted cross-sectional analyses of Veterans with SCI/D across all VA facilities in 2006. CKD was defined as an estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m² and categorized by standard eGFR strata. eGFR was calculated in two ways: (a) the Modification of Diet in Renal Disease (MDRD) equation and (b) the MDRD equation + an empirically derived correction factor for SCI/D (MDRD-SCI/D). Logistic regression models were used to examine the relationship between patient characteristics and CKD. Results: Among 9,333 SCI/D Veterans with an available eGFR, the proportion with CKD was substantially higher based on the MDRD-SCI/D equation (35.2%) than based on the MDRD equation (10.2%). In adjusted analyses, while older age (OR for >65 years = 2.53; 95% CI: 2.21–2.89), female sex (OR 2.18; 95% CI: 1.62–2.92), and a non-traumatic cause for injury (OR 1.39; 95% CI: 1.23–1.57) were associated with an increased odds of CKD, black race (OR 0.64; 95% CI: 0.56–0.72) and a duration of injury of ≥10 years (OR 0.76; 95% CI: 0.67–0.86) were associated with a decreased odds of CKD. Diagnostic codes for CKD and nephrology visits were infrequent for SCI/D Veterans with CKD (27.51 and 6.58%, respectively). Conclusion: Using a recently validated version of the MDRD equation with a correction factor for SCI/D, over 1 in 3 Veterans with SCI/D had CKD, which is more than 3-fold higher than when traditional MDRD estimation is used.