# 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.264 Standard  
The H.264 standard [36], also known as MPEG-4 Part 10 or AVC (advanced video coding), was introduced in 2003 as a result of cooperation between the ITU-T Q.6/SG16 Video Coding Experts Group (VCEG) and ISO/IEC Moving Picture Experts Group (MPEG). The team formed in this way is known as the Joint Video Team (JVT). The H.264 standard uses differential compression, in which the current image is created based on one or more previous images, taking into account the differences that occurred between them at that time. In relation to earlier solutions, the H.264 standard uses a number of improvements, on the one hand, allowing a reduction in the bit rate with unchanged image quality, and on the other hand, significantly increasing the demand for computing power during encoding. The degradation of the quality of the video signal encoded in the H.264 standard was assessed in a group of 25 people at home and 45 people in a laboratory. The obtained results of the measurements made under home conditions are presented in Table 1 and graphically in Figure 5, with the laboratory conditions presented in Table 2 and Figure 6. In addition to the MOS mean value, the tables also include the standard deviation values (S), as well as the values of the confidence interval coefficient (\(\delta\)) calculated according to the ITU BT.500 recommendation [1]. The statistical analysis of the results showed that up to a bit rate of 1000 kbps, the resolution does not affect the assessment of the video image quality made at home, while the laboratory measurements show a slightly lower assessment for the resolution of 1920 \(\times\) 1080. Above this bit rate, the video quality depends on the resolution, and as expected, the video signal with a resolution of 1920 \(\times\) 1080 is the highest rated. For this resolution, an MOS rating of at least 4 was achieved in home conditions at a bit rate starting from 2500 kbps and in laboratory conditions from approximately 1500 kbps. On the other hand, for a resolution of 1280 \(\times\) 720, the MOS value of 4 was achieved at home at 3500 kbps and in laboratory conditions at 2000 kbps. Comparing the results of the MOS evaluation obtained in the laboratory and home conditions, it can be seen that viewers rated the video image presented under laboratory conditions more highly; only for the highest resolution at bit rates up to 600 kbps was the opposite MOS result found. Table 3 and Figure 7 show the difference of \(\Delta\)MOS in the evaluation of video quality obtained for measurements made in the laboratory and home conditions according to Formula (1):  
\[\Delta\text{MOS}=\text{MOS}_{\text{L}}-\text{MOS}_{\text{H}}, \tag{1}\]  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Bit Rate** & \multicolumn{3}{c}{**640 \(\times\) 360**} & \multicolumn{3}{c}{**858 \(\times\) 480**} & \multicolumn{3}{c}{**1280 \(\times\) 720**} & \multicolumn{3}{c}{**1920 \(\times\) 1080**} \\ \cline{2-13}
**(kbps)** & **MOS** & **S** & **\(\mathbf{\xi}\)** & **MOS** & **S** & **\(\mathbf{\xi}\)** & **MOS** & **S** & **\(\mathbf{\xi}\)** & **MOS** & **S** & **\(\mathbf{\xi}\)** \\ \hline
300 & 1.33 & 0.48 & 0.15 & 1.21 & 0.42 & 0.13 & 1.16 & 0.43 & 0.13 & 1.05 & 0.32  
where \(\text{MOS}_{\text{L}}\) is the evaluation obtained under laboratory conditions and \(\text{MOS}_{\text{H}}\) is the evaluation obtained under home conditions. 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.