crf wit hevc_nvenc in ffmpeg?

[mathias_freire]

Hi. I am not a professional video editor. I used ffmpeg with x265 to convert my videos a lot. By using it, I was using crf setting to reduce file size. But there is no option like this in hevc_nvenc. What can I use to encode my videos similar to crf? Thanks.

[LigH.de]

The "constant rate factor" is a technology specific to x264/x265. The most similar 1-pass method of NVEnc would be a constant quantizer (-rc constqp), independent of the material's complexity though.

[Selur]

afaik:

-rc vbr_hq -cq XX -b:v 0k -2pass  0

is the nearest to what NVEnc would call 'constant quality'-encoding which should be similar to crf encoding,...

[mathias_freire]

Thanks. ı will try those parameters

[sophisticles]

Unless of course you want to spend the money on Main Concept, who have managed to combine CRF with NVENC:

https://www.mainconcept.com/fileadmin/user_upload/datasheets/HEVC_SDK_DATASHEET.pdf

https://www.mainconcept.com/hybridgpu.html

For those of you that may have trouble understanding the above, Main Concept added CRF to their software encoder a while ago, and then they used NVENC's ability to use external rate control mechanisms to create a hybrid GPU powered encoder that uses CRF.

It's not cheap, but it does exist.

For the record, Intel's QSV also has the ability to use external bit rate control mechanisms, so there's nothing stopping someone from creating a hybrid QSV encoder with CRF.

[LigH.de]

Nice to know, thanks @sophisticles