# Perceptual Quality of Audio-Visual Content with Common Video and Audio Degradations
## 6 Perceptual Experiment 1 (Video-Only)
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**HRC**} & \multirow{2}{*}{**Codec**} & **Bitrate** & **Packet-Loss** & \multicolumn{2}{c}{**Freezing Pauses**} \\  & & **(kbps)** & **Rate (PLR)** & **Number** & **Length** & **Position** \\ \hline HRC1\({}_{E1}\) & H.264 & 500 & 10\% & - & - & - \\ HRC2\({}_{E1}\) & H.265 & 400 & 8\% & - & - & - \\ HRC3\({}_{E1}\) & H.264 & 2000 & 5\% & - & - & - \\ HRC4\({}_{E1}\) & H.265 & 1000 & 3\% & - & - & - \\ HRC5\({}_{E1}\) & H.265 & 8000 & 1\% & - & - & - \\ HRC6\({}_{E1}\) & H.265 & 200 & - & 3 & \(3,3,2\) & \(1,2,3\) \\ HRC7\({}_{E1}\) & H.264 & 800 & - & 3 & \(2,2,3\) & \(1,2,3\) \\ HRC8\({}_{E1}\) & H.265 & 1000 & - & 2 & \(2,2\) & \(2,3\) \\ HRC9\({}_{E1}\) & H.264 & 2000 & - & 2 & \(1,3\) & \(1,3\) \\ HRC10\({}_{E1}\) & H.264 & 16,000 & - & 1 & 2 & 2 \\ ANC1\({}_{E1}\) & H.264 & 64,000 & - & - & - & - \\ ANC2\({}_{E1}\) & H.265 & 32,000 & - & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: HRC and ANC corresponding parameters used in Experiment 1. By observing the Frame-Freezing HRC group in Figure 6a, we notice that HRC8 and HRC9 presented similar results in terms of \(\text{MQS}_{\text{HRC}}\). These values can be explained by revising the corresponding HRC parameters in Table 7. In terms of bitrate, studies show that a video encoded with H.264 at a certain bitrate has approximately the same quality as a video encoded with H.265 using half bitrate [53,60]. Then, for the particular case of HRC8 (Codec = H.265 and BR = 1000 kbps) and HRC9 (Codec = H.264 and BR = 2000 kbps), a certain quality equivalence is expected. In terms of frame-freezing, both HRCs had the same number of pauses; then, it can be inferred that the small \(\text{MQS}_{\text{HRC}}\) difference between HRC8 and HRC9 is due to the position (P) and the length (L) of the pause events. For HRC8, the pauses were inserted at positions '2' and '3', both with a duration of 2 s. Meanwhile, HRC9 had pauses inserted at positions '1' and '3', with a duration of 1 and 3 s, respectively. The slightly better \(\text{MQS}_{\text{HRC}}\) obtained by HRC9 (in comparison to HRC8) can be explained  
Figure 5: Mean Quality Score (MQS), and its respective spread of scores, for the different Hypothetical Reference Circuit (HRC) in Experiment 1. Figure 6: Mean Quality Score (\(\text{MQS}_{\text{HRC}}\)) and Mean Content Score (\(\text{MCS}_{\text{HRC}}\)) for the different Hypothetical Reference Circuit (HRC) in Experiment 1.  
with the results reported in [61], which state that short pauses at the beginning of the video playout (initial loading) are less annoying than the pauses occurring in the middle of the playout (stalling). With regard to the Packet-Loss group in Figure 6a, HRC3 and HRC4 presented similar results in terms of \(\text{MQS}_{\text{HRC}}\). As in the previous case, it can be inferred that the small \(\text{MQS}_{\text{HRC}}\) difference is due to the Packet-Loss ratio (PLR) since a certain equivalence is expected in terms of bitrate (HRC3: Codec = H.264 and BR = 2000 kbps; HRC4: Codec = H.265 and BR = 1000 kbps). Studies have shown that H.265 is more sensitive to packet-loses than H.264 [62; 63]. For this case, HRC3 and HRC4 have different PLRs, 5% and 3%, respectively. Then, the \(\text{MQS}_{\text{HRC}}\) of a higher PLR (5% with H.264 for HRC3) is slightly smaller than the one of a lower PLR (3% with H.265 for HRC4). A comparison across groups shows that the packet-loss has a stronger effect on the perceived quality than the frame-freezing. This can be verified by observing the \(\text{MQS}_{\text{HRC}}\) values from HRC3 versus HRC9 and HRC4 versus HRC8. For these two cases, the coding parameters are exactly the same. The main difference in \(\text{MQS}_{\text{HRC}}\) values is due to the packet-loss and frame-freezing parameters. Then, we conclude that pauses during the video playout were less annoying to the participants than severe visual distortions caused by packet losses.