DNxHR codec is a CBR

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Hilary Glaps

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DNxHR codec is a CBR

PostTue Aug 04, 2020 12:33 pm

Dear ADOBE fans and users of the DNxHR 444 codec.

AVID says the DNxHR codec has a data rate in MB / s for specified frame rate (exact value).
I understand that the DNxHR codec is a CBR /
has constant bit rate.
Therefore, when exporting from e.g. a grading tool does not enable the "Use constant bite rate" tick. Actually, in my opinion, such an option should not be available for the codec!
We have found that in connection with DaVinci Export DNxHR 444 12 bit with "x Use constant bite rate" there are problems with the subsequent import into After Effects or Premiere.

Probably information is given in the files metadata,
that lead to this problem. Without this addition, it should work.

We hope that in the near future the ADOBE problem will be changed from fullrange to legalrange with the wrong interpretation.

Have fun working
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Andrew Kolakowski

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Re: DNxHR codec is a CBR

PostTue Aug 04, 2020 6:57 pm

DNxHR by default is CBR and actually strict CBR (each frame for given mode is 100% same size).
This box in Resolve has no real meaning (it's for ProRes). It should be graded out for DNxHR. As you found out- it only causes problems when ticked and I've seen same issue.
DNxHR can be VBR which is part of its the spec, but I don't think there is any tool generating VBR streams.

Full vs. legal range metadata was/is? also Resolve problem (for MXF only if I remember well). Not sure if it got fixed.
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hugh1988

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Re: DNxHR codec is a CBR

PostThu May 06, 2021 5:50 pm

As of Resolve 17, unticking the 'Use Constant Bit Rate' box will successfully create VBR DNxHR files. It does create much smaller files with seemingly no loss of quality.
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Andrew Kolakowski

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Re: DNxHR codec is a CBR

PostThu May 06, 2021 8:21 pm

Those are rare, but part of DNxHR spec. Engine is quite conservative with VBR-ness bit. Seen it reducing bitrate for easy parts, but not sure if it goes above 'reference' value. If you have many dips to black or easy scenes then you will save on bitrate. In other cases not necessarily.

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