## 6 Objective QoE Evaluation of Cloud Gaming
### Stuttering Events for Correlated vs. Non-Correlated Scenarios  
Based on the subjective analysis feedback, we found that one of the main reasons for the difference in video and game QoEs was stuttering events and input lag. There are instances in games where, because of high PLR and latency, the streaming platform cannot keep up and broadcasts the same frame for a period of time in order to clear the buffer of corrupted packets and catch up with the live streaming. These cause the gameplay to stutter, lowering the overall quality of the experience. However, the video itself does not lose much clarity because the streaming platform does not display distorted frames, but rather keeps showing the same frame for a period of time. Participants said that when the key input had too much lag, due to high network latency and low PLR, the video quality was not affected, but the game was harder to play because of input lag. Participants rated lower game QoE compared to video QoE when the input had too much lag due to high network latency but had a low PLR. This was because high latency made it harder to react to a game scenario but did not affect the video quality.  
Keeping the feedback in mind, it was decided to look at the number of duplicated packets in more detail. We decided to use the number of duplicated packets to find two types of stutter events. One was a short stutter, while the other was a long stutter. A short stutter event is one where the game stutters for 0.2 to 0.3 s, and a long stutter is one where the game is stuck for more than 0.3 s. The reason to look at short events is that, according to studies done in [45], most professional gamers have reaction times less than 0.3 s and would, therefore, suffer in these kinds of events. These events can also point out situations where the recreational player would feel the game to be difficult to play and less smooth than ideal. The long stutter events give an idea of the situations where controlling the gameplay starts to become unplayable.  
Since the games were streamed at 60 frames per second, having 12 to 18 consecutive duplicated frames would give us the short stutter events. More than 18 consecutive duplicated frames would mean the stuttering event was a long one. We used the average number of duplicated packets for each game to find the frequency of stutter events for all of the games in both correlated and non-correlated QoS scenarios, as shown in Table 3.  
Table 3 only shows the average stuttering events for PLRs of 2% and above, as there were no stuttering events of at least 0.2 s for lower PLR scenarios. In most circumstances, the frequency of short and long stuttering events was greater in correlated scenarios than in non-correlated ones. This applied to each of the three games. This supported the results of the subjective assessment, in which the participants experienced parts of extremely smooth gameplay and parts of extremely tough gameplay due to stutter events in correlated scenarios. This demonstrated how packets were lost during bursts in correlated QoS metric networks, resulting in more frequent stuttering events, and affecting the game QoE more than in non-correlated scenarios.