# Keyframe Insertion: Enabling Low-Latency Random Access and Packet Loss Repair
## 4 Results
### Impact on Quality
#### 4.3.1 VMAF Decrease  
First, the quality is evaluated in-depth on a single sequence. That is, Figure 4 shows the VMAF scores of the _ParkScene_-sequence, for \(\text{NS}_{\text{src}}\), and for \(\text{KI}_{\text{src}}\), and \(\text{KI}_{\text{NS}}\). The videos are encoded with \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=22\). As the keyframe is inserted at the 10 th frame, the VMAF scores are equal in the first 9 frames. At the 10 th frame, the switch in \(\text{KI}_{\text{src}}\) causes an increase in quality compared to \(\text{NS}_{\text{src}}\). That is because the inserted keyframe is of a higher quality (and larger frame size) than the inter-frame that it replaced. However, this quality increase is quickly negated in the subsequent inter-frames; the quality decreases compared to the non-switched video. That is because these subsequent frames expect a different frame as reference. Even though the quality of the reference has increased, the predictions are wrong and hence errors are introduced. After a few seconds, the decrease in VMAF score compared to \(\text{NS}_{\text{src}}\) stabilizes around 0.47. On average over the whole video (excluding the first 9 frames), the VMAF score decreases with 0.63. In case of \(\text{KI}_{\text{NS}}\), the keyframe insertion at the 10 th frame immediately causes a decrease in quality compared to \(\text{NS}_{\text{src}}\). In other words, the opposite effect of \(\text{KI}_{\text{src}}\) is observed. That is because the inserted keyframe was encoded with \(\text{NS}_{\text{src}}\) as input, and thus is inherently of a lower quality than the input itself. Although the inserted keyframe of \(\text{KI}_{\text{NS}}\) initially decreases the quality of the video, the subsequent frames do not further decrease the quality significantly. Starting from the 14 th frame, \(\text{KI}_{\text{NS}}\) even has a better quality than \(\text{KI}_{\text{src}}\). That is because \(\text{KI}_{\text{NS}}\) is closer to the reference that the subsequent inter-frames expect for their predictions. Therefore, the errors that they introduce are smaller than those in \(\text{KI}_{\text{src}}\). After a few seconds, the difference in VMAF score compared to \(\text{NS}_{\text{src}}\) stabilizes to approximately 0.36. On average over the whole video (excluding the first 9 frames), the VMAF score decreases with 0.45. In other words, using the encoded \(\text{NS}_{\text{src}}\) video as input for the inserted keyframe results in a smaller average quality decrease than using the source as input. To additionally analyze the effect of keyframe insertion on a video with lower quality in depth, Figure 5 shows the VMAF scores for the same sequence as Figure 4, but encoded with \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=32\). Because of the higher QP, the effects that were observed in Figure 4 are more pronounced. That is, the initial quality increase of \(\text{KI}_{\text{src}}\) is much larger: the VMAF score increases with approximately 6 points. Then, until frame #28, the quality remains higher than \(\text{NS}_{\text{src}}\) and \(\text{KI}_{\text{NS}}\). Afterward, the quality from \(\text{KI}_{\text{src}}\) drops below the quality of \(\text{KI}_{\text{NS}}\). On average, and over all frames (excluding the first 9 frames), the VMAF score decrease of \(\text{KI}_{\text{src}}\) is 1.1, whereas it is only 0.6 for \(\text{KI}_{\text{NS}}\). In other words, the quality decrease of \(\text{KI}_{\text{NS}}\) is smaller on average, yet the first frames after keyframe insertion of \(\text{KI}_{\text{src}}\) are of higher quality. To summarize the impact on the quality for multiple sequences and QP values, Table 2 shows the decrease in VMAF score averaged over all frames and over all tested sequences,  
Figure 4: Video Multimethod Assessment Fusion (VMAF) scores of the _ParkScene_-sequence, encoded with \(\text{QP}_{\text{NS}}=\text{QP}_{\text{CS}}=22\). On average, \(\text{KI}_{\text{NS}}\) has a smaller quality decrease than \(\text{KI}_{\text{src}}\). for both KIsrc and KINS, for all QPNS, and for all QPCS.