Bit Rate (BR)

As shown in Figure 7.4 through Figure 7.7, the parameter BR exhibits a great influence on the quality. From Figure 7.4, MOS values vary from 3 to 6.7 for (FR=6 fps, LR=0 %, CLP=2, and RA=0.1) and from 3.7 to 7.7 when the FR goes up to 30 fps. This is for a variation of the BR from 0.15 to 0.8. Its effect is comparable to the effect of LR as shown in Figure 7.5. The improvement of the quality is significant for lower LR and decreases for higher LR values. The quality goes from 2.8 to 7.8 for zero loss, but it only presents about 1.3 of absolute improvement for a 10 % LR. The fact that in Figure 7.6 there is no effect of CLP on the quality comes simply from the setting LR = 0.0 %. This shows how well the NN learned the problem of evaluating the quality. From Figure 7.7, for higher values of the BR, there is no effect of the variations of the RA parameter on the quality; however, its effect increases and becomes benefic for lower values of BR. When the encoder has to decrease the BR of the given stream, it increases the quantization parameter in order to compress further the original image. This process increases the artifacts of the output stream, and hence increases the distortion which becomes more noticeable by humans as the BR decreases. This parameter is studied in [153,102]; however, the interaction with other parameters is not shown.

Figure 7.4: The impact of BR and FR on video quality.

  

Figure 7.5: The impact of BR and LR on video quality.