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Best DNX codec for mastering

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Miguel Infante
Best DNX codec for mastering
on Feb 19, 2014 at 10:37:03 am

Hi all,

I'm new to this forum. My last resource ! since I haven't been able to find a clear answer to my case.
I'm working on a project shot mainly on XDCAM HD @50mb/s. I have transcoded all footage to DNX120 thinking we can work 'offline' on this resolution and also complete the mastering under DNX120.

Is this a good workflow or should I "UpRes" to lets say DNX145 or DNX185 before mastering?

Also,
Is there a clear table /guide to choose DNXcodecs?

Cheers!


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Richard Sanchez
Re: Best DNX codec for mastering
on Feb 19, 2014 at 3:40:21 pm

Their really isn't a clear guide of when to use what DNxHD codec, and why however here is Avid's DNxHD Whitepaper with all the information you could possibly want about DNxHD.

http://www.avid.com/static/resources/US/documents/dnxhd.pdf

Since you mentioned DNxHD185 I'm going to assume you're working in PAL. I work in NTSC so I'll be using equivalent codecs, but I've worked on shows that finished DNxHD145 because of space limitations. I worked fine, but if you have the space it's generally best to finish as high quality as possible. True, XDCAM 50 is already a lower bit rate, but that's also a Long GOP format where DNxHD is an intraframe format. The other thing to note is that the X resolutions denote whether it's 8 bit or 10 bit. So DNxHD185 is 8-bit and DNxHD185x is 10 bit. I believe all version of XDCAM are 8-bit so it probably makes most sense to finish at DNxHD185. The other thing to keep in mind is your client. Some clients require specific codecs for mastering, but in any event if I were you I would master at DNxHD185.

For offline, I would have used DNxHD 36 (If you're working at 25p) or DNxHD 85 (If you're working 50i)

Richard Sanchez
Los Angeles, CA

"We are the facilitators of our own creative evolution." - Bill Hicks


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Miguel Infante
Re: Best DNX codec for mastering
on Feb 19, 2014 at 10:44:20 pm

Thanks Richard,

I should have mentioned before, the project is 50i. The XDCAM is def 8-bit.

I didn't mean to have a offline/online workflow. I knew the editors wanted to work full res and thought I could go DNX120 all the way from offline to mastering. AS per avid guidelines I chose the closest DNX codec as per bitrate to the acquisition bit-rate, If the colour sampling is not changing either why couldn't I master on DNX120?

Migs


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JD Marlow
Re: Best DNX codec for mastering
on May 4, 2014 at 1:38:55 pm

Miguel,

I went through this dilemma recently on a job. We shot 50 mbit MPEG-2 4:2:2 on a Canon C300 (1080 @ 23.976 fps) and transcoded to DNX 80 with the thought of NOT doing an uprez to anything higher. I did this on a show last year with material shot on a Canon 7D and everything worked out fine. No QC kickbacks. But I have thought, with the C300 if going higher to 175 would make any noticeable difference.

I ran this test by re linking to AMA files and re transcoding, then did a comparison in Photoshop between 175x, 80, and 36.

I won't say there is no difference between 80 and 175x. But it is only perceptible to the eye with 4x or 8x blow up of the image. There is some finer pixel-to-pixel detail that can be seen from that vantage. Mainly in noisier low-light areas. But, overall, at 1-to-1, I could not tell the difference. I would encourage you to run your own test similar to this because it probably varies depending on the source material. It also depends on who you are delivering to I suppose. If your client is stringent on quality, maybe hedge your bets by doing the up res. But if it's not going to be a big deal, the lower end may be just fine.

JD Marlow
jd@jdmarlow.com
http://www.jdmarlow.com


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Miguel Infante
Re: Best DNX codec for mastering
on May 5, 2014 at 9:11:20 am

Hey JD,

Thanks for that!

I ended up doing the test. We are using XDcam.

I checked the difference between transcoding to DNx120 vs DNX185 and they native XD CAM.

As you said, there is a difference if you blow it up 8+ times where pixels are quite visible but it does not make a difference for the client. I run it by the online editor too and he seemed happy with it.

Cheers


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