Streaming and User Behaviour in Omnidirectional Videos

Omnidirectional videos (ODVs) have gone beyond the passive paradigm of traditional video, offering higher degrees of immersion and interaction. The revolutionary novelty of this technology is the possibility for users to interact with the surrounding environment, and to feel a sense of engagement and presence in a virtual space. Users are clearly the main driving force of immersive applications and consequentially the services need to be properly tailored to them. In this context, this chapter highlights the importance of the new role of users in ODV streaming applications, and thus the need for understanding their behaviour while navigating within ODVs. A comprehensive overview of the research efforts aimed at advancing ODV streaming systems is also presented. In particular, the state-of-the-art solutions under examination in this chapter are distinguished in terms of system-centric and user-centric streaming approaches: the former approach comes from a quite straightforward extension of well-established solutions for the 2D video pipeline while the latter one takes the benefit of understanding users’ behaviour and enable more personalised ODV streaming

Dynamic Viewport-Adaptive Rendering in Distributed Interactive VR Streaming: Optimizing viewport resolution under latency and viewport orientation constraints

In streaming Virtual Reality to thin clients one of the main concerns is the massive bandwidth requirement of VR video. Additionally, streaming VR requires a low latency of less than 25ms to avoid cybersickness and provide a high Quality of Experience. Since a user is only viewing a portion of the VR content sphere at a time, researchers have leveraged this to increase the relative quality of the user viewport compared to peripheral areas. This way bandwidth can be saved, since the peripheral areas are streamed at a lower bitrate. In streaming $360\degree$ video this has resulted in the common strategy of tiling a video frame and delivering different quality tiles based on current available bandwidth and the user's viewport location. However, such an approach is not suitable for real-time Interactive VR streaming. Furthermore, streaming only the user's viewport results in the user observing unrendered or very low-quality areas at higher latency values. In order to provide a high viewport quality in Interactive VR, we propose the novel method of Dynamic Viewport-Adaptive Rendering. By rotating the frontal direction of the content sphere with the user gaze, we can dynamically render more or less of the peripheral area and thus increase the proportional resolution of the frontal direction in the video frame. We show that DVAR can successfully compensate for different system RTT values while offering a significantly higher viewport resolution than other implementations. We further discuss how DVAR can be easily extended by other optimization methods and discuss how we can incorporate head movement prediction to allow DVAR to optimally determine the amount of peripheral area to render, thus providing an optimal viewport resolution given the system constraints

Virtual transcendence experiences: Exploring technical and design challenges in multi-sensory environments

In this paper 1, we introduce the concept of Virtual Transcendence Experience (VTE) as a response to the interactions of several users sharing several immersive experiences through different media channels. For that, we review the current body of knowledge that has led to the development of a VTE system. This is followed by a discussion of current technical and design challenges that could support the implementation of this concept. This discussion has informed the VTE framework (VTEf), which integrates different layers of experiences, including the role of each user and the technical challenges involved. We conclude this paper with suggestions for two scenarios and recommendations for the implementation of a system that could support VTEs

From Capture to Display: A Survey on Volumetric Video

Volumetric video, which offers immersive viewing experiences, is gaining increasing prominence. With its six degrees of freedom, it provides viewers with greater immersion and interactivity compared to traditional videos. Despite their potential, volumetric video services poses significant challenges. This survey conducts a comprehensive review of the existing literature on volumetric video. We firstly provide a general framework of volumetric video services, followed by a discussion on prerequisites for volumetric video, encompassing representations, open datasets, and quality assessment metrics. Then we delve into the current methodologies for each stage of the volumetric video service pipeline, detailing capturing, compression, transmission, rendering, and display techniques. Lastly, we explore various applications enabled by this pioneering technology and we present an array of research challenges and opportunities in the domain of volumetric video services. This survey aspires to provide a holistic understanding of this burgeoning field and shed light on potential future research trajectories, aiming to bring the vision of volumetric video to fruition.Comment: Submitte

Prediction of Visual Behaviour in Immersive Contents

In the world of broadcasting and streaming, multi-view video provides the ability to present multiple perspectives of the same video sequence, therefore providing to the viewer a sense of immersion in the real-world scene. It can be compared to VR and 360° video, still, there are significant differences, notably in the way that images are acquired: instead of placing the user at the center, presenting the scene around the user in a 360° circle, it uses multiple cameras placed in a 360° circle around the real-world scene of interest, capturing all of the possible perspectives of that scene. Additionally, in relation to VR, it uses natural video sequences and displays. One issue which plagues content streaming of all kinds is the bandwidth requirement which, particularly on VR and multi-view applications, translates into an increase of the required data transmission rate. A possible solution to lower the required bandwidth, would be to limit the number of views to be streamed fully, focusing on those surrounding the area at which the user is keeping his sight. This is proposed by SmoothMV, a multi-view system that uses a non-intrusive head tracking approach to enhance navigation and Quality of Experience (QoE) of the viewer. This system relies on a novel "Hot&Cold" matrix concept to translate head positioning data into viewing angle selections. The main goal of this dissertation focus on the transformation and storage of the data acquired using SmoothMV into datasets. These will be used as training data for a proposed Neural Network, fully integrated within SmoothMV, with the purpose of predicting the interest points on the screen of the users during the playback of multi-view content. The goal behind this effort is to predict possible viewing interests from the user in the near future and optimize bandwidth usage through buffering of adjacent views which could possibly be requested by the user. After concluding the development of this dataset, work in this dissertation will focus on the formulation of a solution to present generated heatmaps of the most viewed areas per video, previously captured using SmoothMV

Understanding user interactivity for the next-generation immersive communication: design, optimisation, and behavioural analysis

Recent technological advances have opened the gate to a novel way to communicate remotely still feeling connected. In these immersive communications, humans are at the centre of virtual or augmented reality with a full sense of immersion and the possibility to interact with the new environment as well as other humans virtually present. These next-generation communication systems hide a huge potential that can invest in major economic sectors. However, they also posed many new technical challenges, mainly due to the new role of the final user: from merely passive to fully active in requesting and interacting with the content. Thus, we need to go beyond the traditional quality of experience research and develop user-centric solutions, in which the whole multimedia experience is tailored to the final interactive user. With this goal in mind, a better understanding of how people interact with immersive content is needed and it is the focus of this thesis. In this thesis, we study the behaviour of interactive users in immersive experiences and its impact on the next-generation multimedia systems. The thesis covers a deep literature review on immersive services and user centric solutions, before develop- ing three main research strands. First, we implement novel tools for behavioural analysis of users navigating in a 3-DoF Virtual Reality (VR) system. In detail, we study behavioural similarities among users by proposing a novel clustering algorithm. We also introduce information-theoretic metrics for quantifying similarities for the same viewer across contents. As second direction, we show the impact and advantages of taking into account user behaviour in immersive systems. Specifically, we formulate optimal user centric solutions i) from a server-side perspective and ii) a navigation aware adaptation logic for VR streaming platforms. We conclude by exploiting the aforementioned behavioural studies towards a more in- interactive immersive technology: a 6-DoF VR. Overall in this thesis, experimental results based on real navigation trajectories show key advantages of understanding any hidden patterns of user interactivity to be eventually exploited in engineering user centric solutions for immersive systems

Quality of experience-centric management of adaptive video streaming services : status and challenges

Video streaming applications currently dominate Internet traffic. Particularly, HTTP Adaptive Streaming ( HAS) has emerged as the dominant standard for streaming videos over the best-effort Internet, thanks to its capability of matching the video quality to the available network resources. In HAS, the video client is equipped with a heuristic that dynamically decides the most suitable quality to stream the content, based on information such as the perceived network bandwidth or the video player buffer status. The goal of this heuristic is to optimize the quality as perceived by the user, the so-called Quality of Experience (QoE). Despite the many advantages brought by the adaptive streaming principle, optimizing users' QoE is far from trivial. Current heuristics are still suboptimal when sudden bandwidth drops occur, especially in wireless environments, thus leading to freezes in the video playout, the main factor influencing users' QoE. This issue is aggravated in case of live events, where the player buffer has to be kept as small as possible in order to reduce the playout delay between the user and the live signal. In light of the above, in recent years, several works have been proposed with the aim of extending the classical purely client-based structure of adaptive video streaming, in order to fully optimize users' QoE. In this article, a survey is presented of research works on this topic together with a classification based on where the optimization takes place. This classification goes beyond client-based heuristics to investigate the usage of server-and network-assisted architectures and of new application and transport layer protocols. In addition, we outline the major challenges currently arising in the field of multimedia delivery, which are going to be of extreme relevance in future years