how to fix the qp value of each frame?

[Bobfan]

I want to fix each frame ( at least frame P) to 25. So I use --qp 25 --qpa 0 and --qp25 --qpa 1, both times I find QP cannot be fixed when encoding yuv to h266. I'd appreciate some help.

[adamjw24]

You would need to edit the QPoffset QPOffsetModelOff QPOffsetModelScale CbQPoffset CrQPoffset QPfactor entries of the FrameN (N in [1-32]) parameters and basically set them either to 0 or to 1.0, as well as set IntraQPOffset to 0. Please just mind that you are breaking the encoder and your results will be bad and not representative of either VVC or VVenC.

[Bobfan]

Thanks very much. You mean edit FrameN in the vvenc/randomaccess_faster.cfg(if I use -preset faster), and then rebuild vvenc? After that, use the following command? vvencFFapp --preset faster --InputFile example.yuv -s 2560x1440 -fr 25 --QP 30 --LambdaFromQpEnable 1 --IntraQPOffset 0 --CbQpOffset 0 --CrQpOffset 0 -b example.h266

[adamjw24]

Yes, first edit the randomaccess_faster.cfg file.

Than no, you don't have to recompile, rather you'd have to use the FFapp, and use the -c rancomaccess_faster.cfg parameter to set the preset options.

The config files are parsed at runtime if specified using the -c option of the FF-app.