how VP9 CRF mode works?

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phantom....@gmail.com

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Jun 28, 2019, 11:09:36 PM6/28/19
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Please, explain how VP9 CRF mode works?

At first I encoded video to Q mode. -crf 24 -b:v 0
.\ffmpeg -i "tos.y4m" -c:v libvpx-vp9  -threads 4 -quality good -cpu-used 2 -g 600 -auto-alt-ref 1 -tile-columns 1 -lag-in-frames 25 -aq-mode 0 -row-mt 1 -crf 24 -b:v 0 -pass 1 -an -y -f webm "tos-q24.mkv"
.\ffmpeg -i "tos.y4m" -c:v libvpx-vp9  -threads 4 -quality good -cpu-used 2 -g 600 -auto-alt-ref 1 -tile-columns 1 -lag-in-frames 25 -aq-mode 0 -row-mt 1 -crf 24 -b:v 0 -pass 2 -an -y -f webm "tos-q24.mkv"
In Q mode I get predictable results. By lowering CRF parameter I'm getting higher bitrate. And vice versa. As I understand same results I get if I set qmin and qmax to 24.

But I don't understand how CRF mode works.
To enable CRF mode I should set -crf 24 -b:v 1000k -minrate 500k -maxrate 2000k
It seems that crf is ignored by codec because whatever I set to crf I always get resulting bitrate as I set in -b:v
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