# Assessment of the Quality of Video Sequences Performed by Viewers at Home and in the Laboratory
## 3 Results and Discussion
### Subjective Quality Assessment of Video Encoded Using H.265 Standard  
The H.265 standard [37], also known as high-efficiency video coding (HEVC), was originally published on 13 April 2013 and is currently the most recent and most efficient video coding system. This standard was created in cooperation between the Video Coding Experts Group (VCEG) and the Moving Picture Experts Group. The H.265 standard ensures the compression of videos in very high resolution (2 K, 4 K, 8 K, etc.) and also allows the use of images with increasingly higher resolutions on mobile devices. The H.265 standard offers up to twice the compression compared to H.264. Video compression is based on motion prediction; that is, when there are no changes to a pixel, the codec references that pixel instead of reproducing it. The motion prediction and compensation procedure have also been improved. Another improvement is the enlargement of the macroblock from 16 \(\times\) 16 pixels (H.264) to 64 \(\times\) 64 pixels, which is especially important in high-definition movies. The quality degradation of the video signal encoded in the H265 standard was evaluated in a group of 35 people, under both home and laboratory conditions. The results of the measurements taken at home are presented in Table 4 and graphically represented in Figure 8, with the laboratory conditions presented in Table 5 and Figure 9. In addition to the mean MOS value, the tables also include the standard deviation (S) and the values of the confidence interval coefficient (\(\delta\)) calculated in accordance with the ITU BT.500 recommendation [1]. The statistical analysis of the results showed that up to a bit rate of 600 kbps, the resolution does not affect the evaluation of video image quality. In turn, by comparing the quality ratings for 1280 \(\times\) 720 and 1920 \(\times\) 1080 resolutions, it can be observed that there is no significant difference in the image quality rating for bit rates up to 900 kbps for home measurements and up to 1000 kbps under laboratory conditions. Above these bit rates, the video quality is clearly resolution dependent. For a video signal with a resolution of 1920 \(\times\) 1080, the MOS rating exceeds the value of 4.0 for the bit rate starting from 2000 kbps for home measurements and approximately 1500 kbps for laboratory measurements. On the other hand, for the resolution of 1280 \(\times\) 720, the MOS value = 4.0 is reached for a bit rate of 3000 kbps for home measurements, and for laboratory measurements for a bit rate of 2000 kbps. Level 4.0 was also exceeded for a resolution of 858 \(\times\) 480 with a bit rate of at least 4500 kbps for the home measurements and 2500 kbps for laboratory measurements. A video signal with a resolution of 640 \(\times\) 360 under home conditions does not reach MOS = 4.0, while under laboratory conditions, starting at 4500 kbps, the MOS reaches a value of 4.0. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Bit  
The statistical analysis of the results obtained using the \(t\)-test showed that at the confidence level of \(\alpha\) = 0.05, there is no basis to accept the hypothesis of the identity of the results obtained under laboratory and home conditions. The \(t\)-test values obtained with the Statistica tool for each resolution are as follows:  
- 640 \(\times\) 360; t = 9.1 \(\times\) t \(\alpha\) = 2.1, at \(\alpha\) = 0.05;  
- 858 \(\times\) 480; t = 10.4 \(>\) t \(\alpha\) = 2.1, at \(\alpha\) = 0.05;  
- 1280 \(\times\) 720; t = 10.9 \(>\) t \(\alpha\) = 2.1, at \(\alpha\) = 0.05;  
- 1920 \(\times\) 1080; t = 7.3 \(>\) t \(\alpha\) = 2.1, at \(\alpha\) = 0.05. It can be concluded that the differences between the MOS values obtained under the laboratory and home conditions are significant. \begin{table}
\begin{tabular}{c c c c c} \hline
**Bit Rate** & \multicolumn{3}{c}{**\(\Delta\)MOS**} \\ \hline
**(kbps)** & **640 \(\times\) 360** & **858 \(\times\) 480** & **1280 \(\times\) 720** & **1920 \(\times\) 1080** \\ \hline  
\hline \end{tabular}
\end{table}