The number of Consecutively Lost Packet (CLP)

As the result obtained for this parameter may seem strange, let us clarify its effects. When keeping all other parameters constant and increasing the value of CLP, the distance between any two consecutive loss occurrences increases. This has two consequences: loss occurrences decrease and consequently the deterioration of frames becomes smaller (i.e. smaller number of frames partially distorted by loss). As it is well known and also shown in our previous analysis of FR, the eye is less sensitive to higher values of FR. Moreover, for each lost packet the past macro-blocs (a portion of the image) are still shown on the screen as a kind of error resilience. Hence, larger values of CLP may introduce deterioration in smaller frames. This is equivalent to smaller LR values but slightly lower FR values. As it was previously shown that the effect of LR is much greater than that of FR, the effect of higher values of CLP is benefic to the quality. This result is in agreement with that obtained in [58], although the authors did not explain the reasons why this happens. Starting by Figure 7.11, and for zero LR, there is no visible effect of CLP on the quality, but as the LR increases the effect of CLP increases up to 0.5 for LR=10.0 %. From Figure 7.13, we can see that there is an improvement of 0.5 of the quality when CLP changes from 1 to 5 for BR=0.7, FR=30 fps and LR=1.0 %. In conclusion, CLP effect is important and comparable to FR's. When CLP increases, quality increases too, particularly in the case of poor conditions (i.e. lower values of BR or higher values of LR), while increasing FR improves quality especially for good conditions (high BR and low LR).

Figure 7.10: The impact of FR and RA on video quality.

  

Figure 7.11: The impact of LR and CLP on video quality.