Conversion of .avi to Apple Prores 422HQ. What is the right Buffer Size value ? Should I change it?


I am trying to convert .avi (raw video, uncompressed) to Apple Prores 422HQ.

In Export, There is a requirement in Codec Tab to set Buffer Size - KiB(1s) while converting. What value should I set ? Is there any requirement for this value that Apple Prores 442 HQ uses ?

Shloud I change it or leave it at 1500.00 KiB and just set the exact Bitrate as my .avi file’s bitrate ?
I would appreciate any help, please ?

Best Regards

Seeing a Buffer option means the Codec tab is in constant bitrate mode. For ProRes (meaning the codec is prores_ks), change the rate control to Quality-based VBR, then set Quality to 100%. This will tell the codec to use whatever bitrate is appropriate for the profile selected by vprofile on the Other tab.

My aim is actually to retain Constant Bitrate mode…

ProRes (as implemented in FFmpeg - this is not the official ProRes encoder by Apple) is not a constant bitrate codec by nature. And neither implementation uses the concept of a buffer… they are better described as capped VBR. As for prores_ks, it has general targets, but those aren’t guaranteed. It depends on the complexity of the video being encoded. Is there a specific reason you’re wanting constant bitrate?

Here is the white paper by Apple. Page 23 has the bitrates that are likely to happen at each resolution+FPS and profile. If Shotcut (prores_ks) is put in VBR at 100% quality, it pretty much lands on these targets, averaging the whole file. But forcing the bitrate directly has potential to constrain the codec, meaning it is unable to create the visually lossless transcode that one would expect from the 422 HQ profile.

It depends on the goal.

ProRes will never look as perfect as an original uncompressed file because ProRes is slightly lossy and compressed. So if it was forced to take up the same file size (due to same bitrate) as the original, all that’s happened is a slightly worse-looking file than the original with no space savings.

If you want perfect transcoding quality and aren’t worried about file size, then a lossless codec like Ut Video may be a better choice, and being compressed, would still be smaller than uncompressed YUV.

If you want the ProRes format but best quality possible, then another option is the prores codec instead of prores_ks, which is kind of like an uncapped version of ProRes that results in very good quality but at higher than standard profile bitrates.

If you need a specific bitrate because a playout server is picky or something, then maybe Average Bitrate mode would be better than Constant Bitrate mode. But that’s generally not the ideal setting for the codec.

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