Received August 5, 2019, accepted August 18, 2019, date of publication August 21, 2019, date of current version September 5, 2019. Digital Object Identifier 10.1109/ACCESS.2019.2936470 Why Is Multimedia Quality of Experience Assessment a Challenging Problem? ZAHID AKHTAR 1, (Senior Member, IEEE), KAMRAN SIDDIQUE2, (Member, IEEE), AJITA RATTANI3, (Member, IEEE), SYAHEERAH LEBAI LUTFI4, AND TIAGO H. FALK 5, (Senior Member, IEEE) 1Department of Computer Science, University of Memphis, Memphis, TN 38152, USA 2Department of Information and Communication Technology, Xiamen University Malaysia, Sepang 43900, Malaysia 3Department of Electrical Engineering and Computer Science, Wichita State University, Wichita, KS 67260, USA 4School of Computer Science, Universiti Sains Malaysia, Penang 11800, Malaysia 5INRS-EMT, University of Quebec, Montreal, QC H5A 1K6, Canada Corresponding authors: Zahid Akhtar ([email protected]) and Kamran Siddique ([email protected]) This work was supported by the Office of Research and Innovation, Xiamen University Malaysia under the XMUM Research Program Cycle 3, under Grant XMUMRF/2019-C3/IECE/0006. ABSTRACT Quality of experience (QoE) assessment occupies a key role in various multimedia networks and applications. Recently, large efforts have been devoted to devise objective QoE metrics that correlate with perceived subjective measurements. Despite recent progress, limited success has been attained. In this paper, we provide some insights on why QoE assessment is so difficult by presenting few major issues as well as a general summary of quality/QoE formation and conception including human auditory and vision systems. Also, potential future research directions are described to discern the path forward. This is an academic and perspective article, which is hoped to complement existing studies and prompt interdisciplinary research. INDEX TERMS Audiovisual perception, data-driven analysis, multimedia quality, objective quality metric, quality of experience, quality of services (QoS). I. INTRODUCTION becoming a paramount and demanding issue in multimedia Multimedia services (e.g., Internet Protocol TeleVision, signal processing and practices. social networks, immersive and virtual reality games, multi- Majority of existing studies on QoE are based on quality media conferencing, etc.) not only have gained importance in assessment (QA) of audio, video or audio-visual modalities this wireless era but also are expected to grow exponentially. that may deteriorate under different processes such as acquisi- Such services and applications may provide poor experience tion, preprocessing, transmission, etc. There exist subjective to a user due to multiple reasons, e.g., network (network and objective QA techniques. In subjective QA schemes, overload) and terminal devices known as quality elements [1]. a bunch of trained/naïve end-users are asked to provide Thus, research and industry communities are devising differ- quality grades [4]–[6]. Whereas, signal fidelity measures ent schemes to understand how users perceive and experience (e.g., packet loss proportions) are utilized in objective meth- degradations, and to subsequently provide them with a better ods to estimate quality. Though objective schemes are fast quality of experience (QoE) [64], [65]. and simple, they are poor indicator of perceived QoE owing to Majority of the multimedia applications are comprised of the fact that they overlook human's multi-media perception as two main elements, i.e., audio and video signals. In spite of well as viewing circumstances [7]. It has been widely agreed latest technical advances, core elements of multimedia are upon that signal fidelity measures alone do not register well still impaired usually by lossy signal encoding (decoding) with human QoE gradings of multimedia contents [7]–[11]. and/or fallible transmission channels, which may lead to poor The QoE decided by humans' perception and contentment quality and user experiences [2], [3]. Accurately estimat- is much more compounded than the statistics that may be ing QoE of the communicated audio-visual modalities will obtained using a typical signal QA method and network help service providers to further ameliorate their networks management system. Since the human auditory and visual and services. In fact, digital signals' QoE assessment is systems are the ultimate receivers and the human evaluator observes the transmitted multimedia contents, user-oriented The associate editor coordinating the review of this article and approving perceptual and cognitive correlates of QoE perception are it for publication was Jinsong Wu. needed that is still a long way odyssey owing to various VOLUME 7, 2019 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/ 117897 Z. Akhtar et al.: Why Is Multimedia QoE Assessment a Challenging Problem? FIGURE 1. Illustration of the different factors furnishing user's QoS and QoE. covariates such as user-, context-, and system factors as also feature' or `a property' or `a degree of excellence' [13], which depicted in Fig.1. Nonetheless, current trends in user-centric nowadays may be called ``character'' of an entity [12]. While experiences and burgeoning of wearables have allowed such few philosophers state that quality could not be elucidated, models to be developed [12] and opening door to future the notion of quality remains controversial in modern phi- innovations. losophy. In multimedia domain, quality is usually utilized QoE is a multidisciplinary domain that needs input from with the engineering objectives, since it is a dominant gauge human science (e.g., psychology, physiology, sociology, neu- for assessing systems, applications or services throughout roscience and cognitive science) and information technology both development and operational stages [12]. All in all, (e.g., digital signal processing, machine learning, computer quality could be contemplated as an umbrella term, as many vision and signal synthesis). There are many issues still open elements play a part in constructing quality's cognizance. in the QoE field. Therefore, this article first presents an For example, covariates like loudness, tone, listening effort, synopsis of various interpretations of quality, QoE formation and intelligibility are critical for audio quality. While, factors and perception including human auditory and vision systems, like image size, packet loss, frame rate, level of audio-visual quality of service (QoS), QoE, quality of perception (QoP), synchronization are pivotal for visual or audiovisual quality. and main issues and research opportunities in this field. All The concepts related to quality have been slowly evolving in all, it is an academic and position paper that is expected and continuously refined leading to several definitions, which to complement prior studies and prod interdisciplinary contrast moderately with one another subject to usage's con- research. text [14]. It is imperative to revisit common expressions from this vantage point, since quality has varying overtones deter- II. WHAT ARE QUALITY, QUALITY OF SERVICE, QUALITY mined by the context where it is utilized and some meanings OF PERCEPTION AND QUALITY OF EXPERIENCE? of those concepts have been progressively lost and deserve A. WHAT IS QUALITY? clarification. Therefore, in the following various interpreta- Quality is a metaphysical notion and viewed as a construct of tions of quality throughout literature are presented: the mind that is simple to comprehend but hard to expound. Definition 1 (Dictionary/Lexical View): ``Measure of excel- According to Merriam Webster dictionary, the term quality lence or state of being free from defects, deficiencies, and comes from Latin word qualitas that refers to `an inherent significant variations'' [15]. 117898 VOLUME 7, 2019 Z. Akhtar et al.: Why Is Multimedia QoE Assessment a Challenging Problem? Definition 2 (Transcendental/Metaphysical View): This product/object's features like ergonomics, efficiency, depend- view reckons quality to be synonymous with innate excel- ability and that are assessed through user's perspective, lence, which can be recognized but not defined. The tran- thereby equating customer/user satisfaction with the qual- scendental view of quality is described as ``::: even though ity. According to it, quality is ``Attribute, characteris- Quality cannot be defined, you know what it is. ::: Quality tic, or property of a thing or phenomenon that can be is neither a part of mind, nor is it a part of matter. It is a observed and interpreted, and may be approximated (quan- third entity, which is independent of the two. ::: Quality isn't tified) but cannot be measured, such as beauty, feel, flavor, a substance. Neither is it a method. It's outside of both. ::: It's taste'' [24]. the goal toward which method is aimed'' [16]. But, suchlike Definition 9 (ISO 9000 View): ISO 9000 is a group of perspective of quality has small empirical use, since it cannot quality management techniques standards, which interprets be computed by professionals and can solely be discerned by quality as ``something that can be determined by comparing virtue of experience. a set of inherent characteristics with a set of requirements Definition 3 (ISO 8402-1986 View): According to ISO of customers and other interested parties [25]. The quality is (International Organization for Standardization) 8402-1986 considered high if attributes meet prerequisites, while it's low standard