Block Level adjustment for Subjective Quality and/or Rate Control

Subjective video quality can be enhanced by tuning QP at the block level, this can be enabled/disabled by the hvsQPEnable parameter. The block is the CTB (coding tree block) for H.265, MB (macroblock) for H.264 and the superblock for AV1. Block level rate control can also be enabled/disabled by the cuLevelRCEnable parameter. Applications can enable both parameters to enable subjective video quality adjustment, and also the block level rate control, at the same time.

hvsQPEnable=0 & cuLevelRCEnable=0: Default settings. Disable CTB QP adjustment.

hvsQPEnable=1: Block level QP adjustment for Subjective Quality only

HVS QP will adjust the QP according to the block complexity of the input image. To follow the sensitivity of the Human Eye system for high complex blocks, the QP will have a small increase; for flat content blocks, the QP will have a small decrease. The method may cause a small decrease in objective quality, or much deviation on the final encoded bit rate.

cuLevelRCEnable=1: Block Level QP adjustment for Stable Bit Rate Control only

In this mode, the rate control will try to control current frame bits within the target range by adjusting the block QP. This mode will have a more stable bit rate.

hvsQPEnable=1 & cuLevelRCEnable=1: Block level QP adjustment for both Subjective Quality and Bit Rate Control