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is there quality loss if i import an exported prores 422 file and export it again as a prores 422 file?

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Angela Anderson
is there quality loss if i import an exported prores 422 file and export it again as a prores 422 file?
on Sep 19, 2012 at 7:04:18 pm

I have a question the I hope someone can answer. I'm working on a 3 channel video installation right now, and I need to check the soundness of my workflow.

I'm editing in a custom sized sequence - 768 x 1440, square pixels, upper field, prores 422

This size is because we have 3 screens - two 4:3 screens and one 4:1.5 screen, which are synched with each other and flow from top to bottom, etc.

Most of the original footage that I'm bringing into the sequence is 1920 x 1080, and there is some archival footage in various formats and some stills every once in a while.

The advantage of bringing the high resolution footage into a standard def sequence is that we can then manipulate the image (scaling for example) without huge quality loss. (this is probably the only good reason) - plus the screens that we use are 4:3.

Ultimately after editing in this 1440 x 768 sequence, we have to divide the footage into the three screens. In order to avoid having to re-align every clip manually when cutting and pasting the clips from the 1440 sequence, what i've done is render out a 768 x 1440 clip with the sequence settings, and then import that clip into a sequence with the exact same settings, except it's 768 x 576, to achieve a 4:3 image. I then render this out again to a quicktime file with the same sequence settings.

My question is: have i somehow lost quality through this two step process to achieve the final video?
I think i haven't, but maybe my thinking is wrong.

Any thoughts on this anyone?

Thanks in advance,
angela


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Jeff Meyer
Re: is there quality loss if i import an exported prores 422 file and export it again as a prores 422 file?
on Sep 22, 2012 at 2:19:16 am

Short answer: no.
Technical answer: yes.

If you look at the white paper on ProRes ( http://images.apple.com/support/finalcutpro/docs/Apple-ProRes-White-Paper-J... ) page 15 tells us that some generation loss will happen with the ProRes422 family, but they hold pretty stable from the 3rd generation onward. For most work this generation loss won't be substantial enough to warrant going to an uncompressed workflow.


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