# Assessment of the Quality of Video Sequences Performed by Viewers at Home and in the Laboratory
## 2 Materials and Methods  
The first step of the research consisted of using the subjective video quality assessment. From many different video quality assessment methods [1; 39; 40; 41; 42], the comparative method Double Stimulus Impairment Scale Method (DSSM) was used in the study. The DSSM is recommended by the International Telecommunication Union (ITU), and the measurement technique is described in the BT.500 recommendation [1]. The evaluation consists of comparing the reference video sequence (reference signal) with the evaluated sequence. The reference signal was presented first and assessed second. The task of the observer (viewer) was to assess the degree of deterioration of the second signal in relation to the first signal. The rating was given on a five-point mean opinion score (MOS) scale, where 5 means invisible quality deterioration, 4--noticeable but not annoying, 3--slightly annoying, 2--annoying, and 1--very annoying [39]. The video sequences were presented to the observers in single pairs (pattern-evaluated sequence). Each pair was assessed separately. The reference and evaluated video sequences were separated by a gray screen presented to the observers for about 2 s.  
Measurements were made for two cases:  
1. Evaluation in the laboratory;
2. Ratings at the viewer's home. The evaluation of video quality for condition 1, that is, in the laboratory, was carried out in a room adapted for the evaluation of video signals, equipped with a 60-inch TV screen. The laboratory room met the requirements of the recommendations of the International Telecommunication Union [1; 39; 43; 44]. Its additional advantage was the fact that all participants in the research knew about it, so it did not affect the distraction of the students related to the adaptation to the location of the research. In turn, the video quality assessment for Case 2 was made in home conditions, i.e., not ideal, but still ensuring the quality assessment by the consumer. All participants in the measurements evaluated the video sequence on high-definition television (HDTV) monitors with a resolution of 1920 \(\times\) 1080 [45]. The standard test material was a 20 s video sequence (without sound) with a resolution of 1920 \(\times\) 1080 pixels in AVI format. The length of the video footage was twice as long as the (minimum) value proposed in [1]. This decision does not negatively affect the results of the subjective assessment, but, in the case of objective evaluation, allows one to calculate quality metrics based on a larger dataset, which, in the case of films with varied dynamics and content of the presented scenes, may positively influence the proper calculation of objective quality metrics, which will be more representative and more correlated with the subjective assessment. However, there are studies that take into account longer video samples. This case was described in [46], where the authors considered 180 s samples for the evaluation of QoE in adaptive video streaming over wireless networks. Longer samples allow for a better evaluation of the quality perceived by users, especially when transmission disturbances may occur irregularly and at relatively longer intervals. The test footage included horse racing start scenes (see Figure 1) [47]. The original sequence was encoded in H.264, H.265, and VP09 with different resolutions and different bit rates. Four resolutions were taken into account in the research: 640 \(\times\) 360 (360p), 858 \(\times\) 480 (480p), 1280 \(\times\) 720 (720p), and 1920 \(\times\) 1080 (1080p). For the coding techniques and a specific resolution, various transmission conditions were simulated with 18 bit rates: 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, and 6000 kbps. The test material was presented to viewers divided into encoding technique and resolution. The test videos with different transmission conditions (bit rate) were randomly presented to the viewers.