True constant quality mode for h264_nvenc and hevc_nvenc?

W

whitepuzzle

New Member
Currently the only way to use true constant quality mode with these encoders is with the FFmpeg custom output mode set to options "rc=vbr b=0 cq=[0-51]", which doesn't work with replay buffer. Is there any plan to add a proper CQ mode to the standard output in the future? VBR and CQP are both inferior for quality-to-filesize ratio.

I did a test game recording with CQ mode and it seems to work just fine without overloading the encoder or anything, so I doubt it's a technical limitation that prevents it from being officially implemented.
 
rockbottom said:
I think you're confused or looking at bad information.
-cq <float> E..V....... Set target quality level (0 to 51, 0 means automatic) for constant quality mode in VBR rate control (from 0 to 51) (default 0)
Click to expand...
Definitely not confused about anything. I was right that CQ (Constant Quality) and CQP (Constant Quantizer Parameter) are not the same thing, however I just did some test encodes with ffmpeg comparing CQ (-rc vbr -b 0 -cq X) and CQP (-rc constqp -qp X) modes for hevc_nvenc and found that, at the same file size, CQ mode actually has worse quality than CQP, at least at lower bitrates. I guess OBS devs don't implement the true CQ mode for a reason? According to information I've read on this forum and other forums, CQ mode should in theory outperform CQP mode. Perhaps that's only true for h264_nvenc which I will test later.
 
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The attached docs are correct for NVENC. CQ is the target quality setting. Your encoder settings are more than likely being rejected. Look at your log.

Try this to start & adjust as needed. H265

preset=hq profile=main tier=high rc=constqp rc-lookahead=0 init_qpI=15 init_qpP=18 init_qpB=20 bf=0 b_ref_mode=disabled refs=4
 
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