Hi,
You can refer to this post:
It is to run in CBR and set vbv-size(virtual buffer size). You may tune vbv-size and check the video quality.
Another property is
preset-level : HW preset level for encoder
flags: readable, writable, changeable only in NULL or READY state
Enum "GstV4L2VideoEncHwPreset" Default: 1, "UltraFastPreset"
(0): DisablePreset - Disable HW-Preset
(1): UltraFastPreset - UltraFastPreset for high perf
(2): FastPreset - FastPreset
(3): MediumPreset - MediumPreset
(4): SlowPreset - SlowPreset
By default it is UltraFastPreset. You may try FastPreset and MediumPreset to have better quality.