Shelley Buchinger

Hierarchical video patching with optimal server bandwidth

Video patching is a way for transporting true video-on-demand, that is, instantaneous without any delay, from a video server to several clients. Instead of sending a unique stream to each newly arriving client, clients share as many multicast transmissions as possible, and are serviced only those parts of the video that they have missed. We present a novel video patching scheme using hierarchies of patches. Our scheme minimizes the bandwidth needed by the video server, and may result in the fact that clients receive several streams in parallel. We show analytically that for Poisson arrival our algorithm achieves the optimal possible server bandwidth for all schemes where clients share multicast transmissions. We also show, how our approach can be combined with batching. This combination requires less server bandwidth than all fixed start point periodic broadcast algorithms.

A survey on user studies and technical aspects of mobile multimedia applications

Abstract Some years ago, Mobile TV has been introduced in several countries all over the world. It was expected that it would play a major role among traditional TV services. Unfortunately, the success has been limited at the beginning. Since Mobile TV brings new aspects into television, like small screens, consumption in noisy surroundings, etc., it also represents a new challenge on how to create, transfer and present content that maximizes the consumer experience. Today, some of these issues have been solved. Due to the introduction of smart phones and the large amount of available applications customers are starting to use their mobile phones for several purposes including mobile multimedia services. As a consequence, the concept for Mobile TV has changed significantly. In the past, research has often been focusing on one particular aspect of this new TV scheme, as well as surveys on this research often neglected aspects that still might be of interest when trying to understand the dependencies of Mobile TV content and presentation to perceived quality. In this survey paper we want to discuss challenges and requirements in a comprehensive way, trying to shed light on all relevant aspects of Mobile TV. The aim of this paper is to give a good overview about the state of the art with the focus of users’ need and experiences. A large collection of technical aspects and research results represents a special interest of this study. Finally, we want to discuss a framework for mobile multimedia applications which is relevant for further research work.

Acceptance of mobile TV channel switching delays

User interaction has always been one of the most crucial points when evaluating the quality of experience of a service. Mobile television, especially when received over DVB-H or in other small bandwidth transmission environments such as UMTS networks, imposes some restrictions to this interaction, since switching from one channel to another requires an indefinite amount of time. It is therefore necessary to describe the technical foundations leading to these delays. Moreover, methods need to be developed to render channel switching times more appealing.

Gesture and touch controlled video player interface for mobile devices

Today, mobile communication devices allow users to access a wide variety of multimedia contents and services. In order to improve user experience and device usability, the design of interfaces and interaction techniques for mobile devices have focused on new modalities, other than those used for desktop computers. In this paper, we describe a novel gesture controlled video player interface for mobile devices. The results of a usability study confirm that users would definitely like to adopt the major part of the proposed features. Furthermore, the responsiveness and reliability of the interface has been studied. Measured response times have been found to be within acceptable boundaries and the number of unrecognised haptic controls is limited.

Loudness and auditory masking compensation for mobile TV

Quality of Experience in mobile multimedia services is subject to environmental changes. Especially in urban environments, several types of background noises affect the perceived quality of audio content, and the characteristics of noise can rapidly change within a few minutes of travel. Also, the change of loudness in the multimedia content itself can be annoying - users will have to adjust volume settings for each specific content type when there is a high dynamic loudness behaviour. It is therefore necessary to automatically adapt the audio playback to the environmental conditions by implementing several methods and testing them. To develop these methods, the impact of environmental noise on the subjective setting of volume needed to be studied by performing a first experiment with human observers. Then, various processing schemes were applied to the audio tracks. These include the decreasing of available headroom as a simple mean of dealing with high loudness dynamics, but also multiband compression alongside noise-specific equalization, which can be used for complex content types such as classical music. Their effect on users perception has been studied by performing two additional user studies.

Optimal server bandwidth for mobile video on demand

Multimedia services such as video-on-demand or Internet protocol television in mobile environments have established themselves in our daily lives, yet the obtained quality of service still leads to many open issues. One of them consists in minimizing the server bandwidth, and we recently proposed a novel patching scheme for transporting true video-on-demand called Hierarchical Patching, which minimizes the server bandwidth. In this paper, we present a new concept called Low Start, consisting of encoding the first part of a movie with a lower bitrate than the rest. In Hierarchical Patching, video parts at the beginning have a much higher probability to be transmitted than parts at the end. By using Low Start, we show that the overall server bandwidth can be drastically reduced. We furthermore investigate the impact of Low Start on the subjective quality of service as perceived by human observers, and show that, for mobile video, the optimal strategy is to encode a very short start time with a bandwidth as low as possible.

Visual attention in edited dynamical images

Edited (or cut) dynamical images are created by changing perspectives in imaging devices, such as videos, or graphical animations. They are abundant in everyday and working life. However little is known about how attention is steered with regard to this material. Here we propose a simple two-step architecture of gaze control for this situation. This model relies on (1) a down-weighting of repeated information contained in optic flow within takes (between cuts), and (2) an up-weighting of repeated information between takes (across cuts). This architecture is both parsimonious and realistic. We outline the evidence speaking for this architecture and also identify the outstanding questions.

Peer to peer mobile TV recovery system

Mobile TV is already available for several years. The provided quality is generally attractive but of course, data transfer is not always optimal. It can be subject to disturbances such as fading, noise or interference that are responsible for temporary quality decreases. In Europe, the common way of realising mobile broadcasting is the implementation of the DVB-H standard without return channel. Until now, the embedded forward error correction MPE-FEC represents the main strategy applied to avoid data loss. The contribution of this paper is twofold: We started by measuring the currently experienced DVB-H loss in a typical urban place at different times a day and with antennas of different quality. This experiment led us to the conclusion that losses are affecting seriously obtained video quality when using a standard antenna of a mobile phone. These losses could be avoided (1) by using a high quality antenna or (2) by implementing a simple recovery strategy. Since the amount of data rates requested tend to increase with time the use of the high quality antenna does not represent a lasting solution. Therefore we decided to propose a new hybrid peer-to-peer recovery strategy combining DVB-H with UMTS connections. We evaluated the recovery mechanism by performing a simulation. Realistic transmission parameter values have been used. We showed that data loss can be significantly reduced with the cost of a marginal amount of waiting time increase.

Guest editorial: Advances in tools, techniques and practices for multimedia QoE

It has been realized that the success of multimedia services or applications relies on the analysis of the entire user experience (UX). The relevance of this paradigm ranges from Internet protocol television to video-on-demand systems for distributing and sharing professional television (TV) and user-generated content that is consumed and produced ubiquitously. To obtain a pleasurable user experience, a large amount of aspects have to be taken into account. Major challenges in this context include the identification of relevant UX factors and the quantification of their influence on Quality of Experience (QoE). This special issue is dedicated to advances in, tools, techniques and practices for multimedia QoE that tackle several of the aforementioned challenges.

Evaluating feedback devices for time-continuous mobile multimedia quality assessment

In January 2014, the new ITU-T P.913 recommendation for measuring subjective video, audio and multimedia quality in any environment has been published. This document does not contain any time-continuous subjective method. However, environmental parameter values are changing continuously in a majority of outdoor and also most indoor environments. To be aware of their impact on the perceived quality, a time-continuous quality assessment methodology is necessary. In previous standards, targeting laboratory-based test settings, a desk-mounted slider of substantial size is recommended. Unfortunately, there are many environments where such a device cannot be used.In this paper, new feedback tools for mobile time-continuous rating are presented and analysed. We developed several alternatives to the generally adopted desk-mounted slider as a rating device. In order to compare the tools, we defined a number of performance measures that can be used in further studies. The suitability and efficacy of the rating scheme based on measurable parameters as well as user opinions is compared. One method, the finger count, seems to outperform the others from all points of view. It was been judged to be easy to use with low potential for distractions. Furthermore, it reaches a similar precision level as the slider, while requiring lower user reaction and scoring times. Low reaction times are particularly important for time-continuous quality assessment, where the reliability of a mapping between impairments and user ratings plays an essential role. HighlightsWe developed a scheme to objectively compare subjective rating methods.We tested this scheme by comparing several rating devices.Users would like to express experienced quality with a simple finger count method.The finger count method outperformed other approaches also objectively.Haptic feed-back distracts the user from his task instead of providing help.