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Reconforming to original H.264 after editing 5D footage in ProRes 422?

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Zak Stoltz
Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 15, 2010 at 11:44:51 pm

The company I work with just finished some commercials shot on the 5D. Essentially, the post-production workflow (using Mac and Final Cut Studio) was as follows:

Transcode original H.264 files to ProRes 422.
Edit with ProRes 422.
Reconform edits to original H.264 footage.
Export as Uncompressed 10-bit HD.
Send to post-house for CC, effects, etc.

Based on the research I've done so far, I am starting to wonder if it's even necessary to reconform to the H.264 footage before exporting uncompressed. Is there anything to be gained by doing so? Would there be a degradation of quality if instead of going H.264>Uncompressed, we went H.264>ProRes>Uncompressed?

I've been reading up on these forums and elsewhere a LOT, and it sounds like a majority of people are saying that it's not worth transcoding 5D footage to ProRes 422 (HQ)-- that regular old ProRes 422 will suffice. Is this because people are mastering in ProRes, and the quality difference between 422 and 422 (HQ) is negligible?

What do YOU think?


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cow
Michael Sacci
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 15, 2010 at 11:52:41 pm

You cannot edit or color correct H264 footage. It has to be transcode before you start editing.


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Zak Stoltz
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 1:29:48 am

Yes, I'm aware of this. If you had read my post more closely, you would see that we are currently editing in ProRes 422 and color correcting Uncompressed HD footage. If you would like to address my original question, I encourage you to go back and read the original post.


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Michael Sacci
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 2:58:06 am

So you are asking if you should go from H264 to ProRes to H264 to Uncompressed. I have never seen anyone recommend the step back to H264 and you should never do that. That is adding a layer of major compression again to the process.


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Zak Stoltz
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 7:39:39 am

I'm afraid you're still not getting it. The native recording format for the 5D is H.264. First we take the original H.264 footage and transcode it to ProRes 422 to edit. Then, once we are done editing, we replacing the transcoded footage with the original footage before exporting it as uncompressed HD. It's like an online/offline edit. Get it?

So the question then becomes whether or not it makes sense to go back to the original footage as opposed to staying in ProRes before going uncompressed.

It's the difference between...

[Original H.264] --> [Uncompressed HD]

and

[Original H.264] --> [ProRes 422] --> [Uncompressed HD]

Will the second method listed result in noticeably lesser video quality than the first method?


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cowcowcow
Michael Sacci
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 8:33:19 am

I guess I was reading to much into the post. If you want to do it, why not, most people will not even go to the uncompressed codec at all. But maybe that is what your finishing people want. But do some test, if you think you are gaining something do it. I would not even bother, I would keep it ProRes to the end.


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cowcowcowcow
Uli Plank
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 3:29:23 pm

The initial H.264 compression is so destructive, you won't see any difference. Just wasting space!

Director of the Institute of Media Research (IMF) at Braunschweig University of Arts


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cowcowcowcowcow
Dave LaRonde
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 4:07:12 pm

[Zak Stoltz] "Reconform edits to original H.264 footage. "

Once you're in ProRes, this step is unnecessary, and just wastes time. Leave it as ProRes, and image quality will not suffer one bit.




[Zak Stoltz] "Export as Uncompressed 10-bit HD.
Send to post-house for CC, effects, etc. "


Yup. If the post houses can't use ProRes HQ, which holds up better in re-rendering situations, Uncompressed 10-bit is a solid choice.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Zak Stoltz
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 5:29:31 pm

Thanks for the input, guys. This is what I've always thought, but the higher-ups at my company don't seem to share that view...

Does anyone know of a definitive test or example that proves reconforming to H.264 is unnecessary? I'm trying to convince the decision makers here that, as Dave said, it's a waste of time. :-)

Also, if anyone disagrees, and thinks it WOULD be beneficial to go back to the original H.264 footage, I'd like to hear from them as well.


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Dave LaRonde
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 6:20:41 pm

[Zak Stoltz] "Does anyone know of a definitive test or example that proves reconforming to H.264 is unnecessary? I'm trying to convince the decision makers here that, as Dave said, it's a waste of time. :-) "

I'm aware of an Apple White Paper on the ProRes family of codecs from July 2009, but there were no comparisons to anything like 10-bit uncompressed.

But there's this for the Powers That Be to consider: ProRes is a 10-bit codec. H.264 is capable of 10-bit, but does the 5D actually make 10-bit files? If yes, then great -- you lose no image quality when converting the files. A no answer is irrelevant: You obviously lose no quality, plus you have the luxury of editing in 10-bit, which is significant when you export.

When you're ready to export to 10-bit Uncompressed, you do NO re-rendering. You don't have to when you use ProRes 422. You go from 10-bit to 10-bit. You simply convert to 10-bit Uncompressed.

To summarize: you lose NO image quality going from H.264 to ProRes 422. There is NO generational loss going from ProRes 422 to 10-Bit Uncompressed.

So here's the question for The Boss: How will the additional step of converting ProRes 422 back to H.264 for subsequent conversion to 10-Bit Uncompressed improve the image quality of a workflow that suffers no loss of image quality?

I suppose that for the true image quality obsessive-compulsives among us, the needless measure of using ProRes HQ instead ProRes 422 would be fine. Overkill, but just fine: you can still easily edit with it.

Hey, The Boss buying the storage, right? If he/she wants to fill it up with unnecessarily-large video files, I say he/she has every right to do so. Furthermore, if it gets you out of that goofy H.264>ProRes 422>H.264>10-Bit Uncompressed workflow, it's worth every extra gigabyte it takes.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Chris Tompkins
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 7:26:26 pm

Why do they want to re-compress the footage further degrading it when it's edited and finished?
To use as a deliverable?



Chris Tompkins
Video Atlanta


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Dave LaRonde
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 16, 2010 at 7:30:27 pm

[Chris Tompkins] "Why do they want to re-compress the footage further degrading it when it's edited and finished?"

They don't -- they want to replace the edited ProRes 422 clips in the FCP edit timeline with the original H.264 files from the 5D, then export to 10-bit Uncompressed. They think they'll get a little more image quality.

Screwy, huh?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Zak Stoltz
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 17, 2010 at 12:12:37 am

Haha, thanks for saving me that explanation again, Dave. Chris is the second person to misunderstand what I'm talking about. I wonder, is "reconform" the wrong word to use when talking of replacing the ProRes with the original H.264?

In my quest to convince the powers that be to cut out the inefficiency in their workflow, I performed a couple of tests and got some very, VERY interesting results:

Using the Canon EOS plugin for FCP, I transcoded a clip from H.264 to ProRes 422 and compared the gamma, color, and sharpness by "stacking" the original footage and the ProRes one on top of the other and switching back and forth between them at various zoom levels. In terms of gamma and color, they're IDENTICAL.

Also, I'm not exactly sure how it happened, but it looks like sharpness is actually INCREASED when transcoding from H.264 to ProRes, and that increased sharpness carries over into the final uncompressed 10 bit exports!

After performing the same tests with 10 bit uncompressed exports (one coming directly from the source footage and the other coming from the ProRes transcode), the one coming from ProRes was still the clear winner.

Thanks for the input everyone. Looks like this case is closed.


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Doug Beal
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 17, 2010 at 5:19:22 pm

is "reconform" the wrong word to use when talking of replacing the ProRes with the original H.264?
Yes the operation you describe would be called a conform. Usually used for an offline/online situation where an offline codec is used to edit, then an xml, EDL or reconnection of media using the highest quality available source footage takes place based on the TC/reel number from the edit.

reconform would assume a conform had taken place already and you were doing it again.
you have merely transcoded then edited in your case.

Glad you were able to convince your people to skip the return to h264. Totally unnecessary.

Doug Beal
Editor / Engineer
Rock Creative Images
Nashville TN


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ryan loetscher
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Jul 29, 2010 at 10:08:59 pm

I dont know if anyone is going to read this at this point, but it seems there's a lot of work going into pointless quality testing. As I understand it, you convert to ProRes so you can edit because H.264 is horribly taxing on your CPU due to its extensive GOP structure and compression techniques. There will be no actual QUALITY difference between your H.264 and ProRes, or even Uncompressed. You cant increase quality that's not there. Now, once you do color and other effects, it makes sense to go out to a higher quality codec so you don't lose any information you just added. ProRes would probably be fine... if your doing extensive color grading it might make sense to use the 4:4:4 flavor. But there's an argument not to go back to H.264 right there, those original files don't have the same color space at 4:2:0 with predictive frames to faithfully hold all the information you just added (of course I'm not sure how accurate that part is, but it sounds convincing!)



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nthabi serote
Re: Reconforming to original H.264 after editing 5D footage in ProRes 422?
on Apr 26, 2012 at 9:51:21 am

ok this all sounds like something i know, yes you cannot work on h264 files, but i have 5D transcoded footage and it seems i can not go back from here, i have also checked on mpeg streamclip to see if there is anyway i can go back to the original file, but i cant, i would have to compress it AGAIN! but i need to get back to the original file and i dont have the drive with the original footage on it, I would like to cheat the system and make proxy files with the current format i have (prores 4444).

is there any way i can take it back without messing up the quality?


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