# Multi-Layer QoE Learning System Implemented by Fiberhost
## 5 Implementation of Unsupervised Learning
### Clustering  
Unsupervised techniques were used due to the lack of reliable labels related to the assessment of perceived video quality. For stream clustering, we used the input features described in [24], and computed on the basis of the characteristics of adaptive video content streamed over the HTTP protocol. This is the technology used by the TV system to deliver video content to customers. Specific TV channels are delivered to clients at different quality levels. CDN servers can typically stream three or four profiles per channel. In general, the higher the bitrate, the better the quality and resolution of the video content. Standard channels can range from 800 kbps to 10 Mbps per profile. Beyond these values, there are usually 4 K (3840 \(\times\) 2160) resolution channels. The _SCI_ (1) parameter takes on values between the range \(<-1;1>\) and determines the degree to which the video profile changes during playback. If the player switches to a higher profile, i.e., one with better quality from the viewer's point of view, the parameter takes on positive values. In the opposite case, it will take on negative values. If the player starts playing the highest profile available for a given channel, then \(SCI=1\). If the player is unable to play any stream, e.g., due to network degradation at the customer's home, then \(SCI=-1\). \[SCI= \begin{cases}-1&bitrate_{kps}^{N}=0\\ 1&bitrate_{kps}^{N}=ref_{bitrate}\\ \frac{bitrate_{kps}^{N}-bitrate_{kps}^{N-1}}{ref_{bitrate}}&\text{ otherwise.}\end{cases}  \tag{1}\]  
_SCT1_ (2) is a correlated coefficient with SCI to determine the level of distortion on a given channel over time. This coefficient takes into account the importance of a given _channel viewership_\({}^{T}_{CH}\) (3) by comparing the ratio of active decoders on the selected channel \begin{table}
\begin{tabular}{l c c} \hline \hline
**Grade** & **Estimated Quality (ACR)** & **Perceived Impairment (DCR)** \\ \hline
5 & Excellent & Imperceptible \\
4 & Good & Perceptible but not annoying \\
3 & Fair & Slightly annoying \\
2 & Poor & Annoying \\
1 & Bad & Very annoying \\ \hline \hline \end{tabular}
\end{table} 
Table 4: ITU-T 5 point ACR and DCR scale. Figure 10: Outline of QoE assessment system for OTT TV service. The red shape indicates the unsupervised part. \(CH\) to all active set-top boxes at a given time. Viewership is calculated at time intervals fixed at \(TI=15\) minutes but can be adjusted accordingly. \(SCTI\) takes into account the playback time of a given stream. This parameter will be negative when playing a lower bitrate profile. The parameter \(edt_{n}=t_{n}-t_{n-1}\) indicates the playback time of the stream. If a stream with a lower quality than the maximum is played for a longer time, the SCTI parameter will be further amplified to reach lower values. The reason for the inclusion of channel viewership is that some channels may be more important than others from a provider perspective. When major events are broadcast on television, the number of viewers tends to increase significantly. A degradation or even failure during such an event could lead to a significant reduction in the viewer's perceived quality of the overall service. \[SCTI=\log_{2}(1+edt_{n})\cdot SCT\cdot\left(1+channel\ viewership_{CH}^{TI}\right) \tag{2}\]  
\[channel\ viewership_{CH}^{TI}=\frac{active\ devices_{CH}^{TI}}{all\ active\ devices_{CH}^{TI}}. \tag{3}\]  
\(VSBCT\) (4) is a memory factor that takes into account the frequency of profile changes and stalls. A large number of events in a short period of time can have a greater effect on the perceived quality of the video than a small number of individual events that occur over the entire playback session. Any negative change in quality will cause this ratio to deteriorate. Conversely, a passage of time without negative events causes the coefficient to increase. A large number of events in a short period of time will cause this indicator to decrease significantly.