# Keyframe Insertion: Enabling Low-Latency Random Access and Packet Loss Repair
## 4 Results
### Drift-Error Artifacts Analysis  
This section briefly analyzes the artifacts that are introduced due to keyframe insertion, of which the errors drift throughout the GOP.  
First, Figure 7c shows the frames corresponding to Figure 4, i.e., from the _ParkScene_-sequence, encoded with \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=22\). More specifically, frame #28 of \(\text{NS}_{\text{src}}\) and \(\text{KI}_{\text{src}}\) is shown, as it corresponds to the largest VMAF score decrease in that sequence, for those QP values (1.29 VMAF points). Additionally, the differences are visualized in Figure 7c, which shows the Y-channel differences using the absolute pixel value difference, and a pixel value is represented by 8 bits. It is quite hard to spot any artifacts in Figure 7b,  
\begin{table}
\begin{tabular}{l r r r r r r r} \hline \hline  & & \multicolumn{6}{c}{**Worst-Case VMAF Score Decrease**} \\ \cline{3-8}
**QP\({}_{\text{CS}}\)** & & \multicolumn{2}{c}{\(\text{KI}_{\text{src}}\)} & \multicolumn{2}{c}{\(\text{KI}_{\text{NS}}\)} & \\ \hline  & **QP\({}_{\text{NS}}\)** = & **22** & **27** & **32** & **37** & **22** & **27** & **32** & **37** \\ \hline
22 & & **4.45** & 4.97 & 6.60 & 6.48 & **3.08** & 2.96 & 1.22 & 1.41 \\
27 & & 4.22 & **4.45** & 6.52 & 6.80 & 3.43 & **4.31** & 2.51 & 1.26 \\
32 & & 6.49 & 6.18 & **7.15** & 6.77 & 6.50 & 7.01 & **3.04** & 2.02 \\
37 & & 13.40 & 9.03 & 7.32 & **7.52** & 14.39 & 11.01 & 7.83 & **5.17** \\ \hline \hline \end{tabular}
\end{table}
Table 6: Worst-case decrease in VMAF score.  
Figure 6: VMAF score decreases of \(\text{KI}_{\text{src}}\) of all tested sequence, encoded with \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=22\).  
even with aid of the visualization of the differences in Figure 7c. In general, most artifacts are in areas with a lot of texture, such as in the leaves of the plants and trees. As the human eye is least sensitive to changes in areas with a high spatial frequency, these artifacts are generally imperceptible.  
To more extensively analyze potential drift-error artifacts, one of the worst cases is investigated. Figure 8 shows the frames corresponding to the worst-case VMAF decrease reported in Table 6, of \(\text{NS}_{\text{src}}\) and \(\text{KI}_{\text{src}}\), for \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=27\). More specifically, the VMAF score decrease is 4.45 for the _BQSquare_-sequence at frame #360. At first sight, one may not notice any objectionable artifacts. However, upon close inspection, some local artefacts are visible. For example, color bleeding from the top-right red umbrella into the water can be observed. Moreover, the shadow of the right chair under the top-right umbrella became brighter. Furthermore, an additional shadow is introduced for the right chair of the top-left table without umbrella. Thus, in general, these artifacts are visible upon close inspection but may not even be noticed without reference to the original frame. As a final note, it is important to keep in mind that these artifacts correspond to the worst-case quality decrease. In general, on average, the quality decrease is an order of magnitude smaller, and thus even less perceptible.  
Figure 7: Frames of the _ParkScene_-sequence with \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=27\). (**a**) The frame of \(\text{NS}_{\text{src}}\) without drift-error artifacts. (**b**) The frame of \(\text{KI}_{\text{src}}\) with drift-error artifacts. (**c**) The differences between subfigures (**a,b**). It is recommended to view these images in color, digitally.