# Assessment of the Quality of Video Sequences Performed by Viewers at Home and in the Laboratory
## 1 Introduction  
For many years, in everyday life, television played the role of the most important medium. Significant changes are currently being observed, especially among the young generation. Today's youth are increasingly willing to watch TV broadcasts, including movies, via the Internet using mobile devices or laptops. An important issue is the quality of the video delivered to the users. There are two general approaches to quality assessment, namely, subjective and objective. The recommendations of the International Telecommunication Union (ITU) [1] specify, in detail, the conditions for performing measurements related to the subjective assessment of video quality. In general, the assessment should be conducted under laboratory conditions, possibly simulating home conditions. The universal measurement room should be able to meet the requirements of an idealized room as well as a domestic room. Recommendation BT.500 [1] defines the general viewing conditions for subjective assessments in a laboratory and in the home environment. However, it shouldbe taken into account that the general viewing conditions for the home environment do not guarantee that they will suit the specific home conditions of each user. An Internet user usually watches a video transmission under conditions that do not always meet the requirements of the ITU BT.500 recommendation. Consequently, the evaluation of video quality performed under real home conditions and under home conditions emulated in the laboratory will not necessarily be the same. Moreover, conducting the research in real users' locations allows us to spread the test environment across a much wider population of service customers. In general, the viewing conditions can significantly impact the results obtained. The purpose of the evaluation and the audience to whom the evaluation is devoted may determine the acceptable circumstances of the test. The next issue of such a subjective evaluation is its high cost, because many factors must be included in the experimental design and many subjects (human testers) must be involved. Therefore, many studies try to find a replacement for these methods by modeling, simulating the real world in an artificial environment, or using objective approaches to quality assessment [2]. In the next step, different approaches to quality modeling may be applied, taking into account the different points of view of various stakeholders in the media streaming process [3]. However, the results obtained from objective methods may not always correlate with subjective users' scores, especially when the circumstances of subjective quality assessment are changing. The authors anticipate that the video quality assessment performed in the artificial environment (even if the conditions emulate an 'average' home) may give different results from the scores obtained under real home conditions. Examining this may provide an answer as to whether the assessment of video quality experienced by users may (or may not) always be replaced by laboratory tests. The next issue occurs when we talk about comparisons between the subjective and objective results of the quality assessment. This is not a trivial task, taking into account that there are plenty of objective methods and quality metrics. There is a long list of literature that describes their characteristics. Some studies discuss their strengths and weaknesses, as well as their usability to predict video quality assessed by end users, especially when talking about metrics such as mean squared error (MSE) and peak signal-to-noise ratio (PSNR) [4; 5; 6]. Others show that the correspondence between objective and subjective scores also depends on the video content and show that some metrics, such as the structural similarity (SSIM) index, present characteristics similar to the human visual system (HVS) and their results are closer to users' subjective scores [7; 8].