Why is CQP level multiplied for AV1 NVENC encoder

[Bleuzen]

FFmpeg says the QP levels for the AV1 NVENC encoder go from -1 to 255, see:
ffmpeg -hide_banner -h encoder=av1_nvenc

However in OBS the max level in CQP mode for AV1 is 63:

Looking at the code, this value is later multiplied by 4:

obs-studio/plugins/obs-ffmpeg/obs-nvenc.c

Line 671 in c25f059

int cqp_val = enc->codec == CODEC_AV1 ? cqp * 4 : cqp;

Why not expose the raw value like it is done for the other codecs?

[RytoEX]

AOM and SVT-AV1 both map values 0-63 to 0-255 internally. Multiplying 0-63 by 4 gives a close enough approximation (all values are equivalent except for the mappings for 62 and 63) and, realistically, no one is or should be selecting the higher values.

https://aomedia.googlesource.com/aom/+/refs/tags/v3.8.1/av1/encoder/av1_quantize.c#895
https://gitlab.com/AOMediaCodec/SVT-AV1/-/blob/v1.8.0/Source/Lib/Encoder/Codec/EbModeDecisionProcess.h#L1278-1283