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CBR vs VBR in master archive exports

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Juan Juig
CBR vs VBR in master archive exports
on May 13, 2020 at 11:37:03 pm


on the film acady that I went to they always told us to export the final master archive files in DNxHD or DNxHR codecs. I always did so, but lately started wondering about different characteristics of the exports, especially bitrate.

To my understanding all DNxHD and DNxHR codecs are strict CBR, while the ProRes files are VBR.

Since I work on Windows machines most of the times, DNxHD and DNxHR are definitely better options for me, but I read some articles about CBR vs. VBR and many claim that VBR is always better, since it distributes bitrate among frames unevenly. Now, am I right to assume, that this mostly applies to smaller files, like h264 files with low bitrate? I tend to export those VBR 2-pass.

However, when it comes to master archive files I assume CBR is a completely viable option, since DNxHD and DNxHR only offer this sort of encoding? So far I have always exported my files in either DNxHD 185x or DNxHR 444.

My ultimate question is: could CBR encoding theoretically result in unacceptable quality loss and visual "pumping" (visible changes in quality over time) of Picture in scenes, where a lot of information is needed to encode (action scenes with a lot of details for example) or is that in practice unnoticable and neglectable with files that have high birate?

Let's take DNxHD 185x as an example. Is 185Mbps a bitrate high enough that what I described above is something not to worry about? With VBR it could for example encode something more demanding at 300Mbps and something less demanding at 100Mbps. Is VBR more acceptable with master archive files or is CBR even better, since there is more constantcy?

I'm assuming, since DNxHD and DNxHR which are widely used for archiving, my question might be nitpicking, but I would really appreciate a definite and reassuring answer.

Thank you

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