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Transcoding to DNxHD decreases quality
I started editing on Adobe Premiere CS6 but later switched to Avid Media Composer 6.5 for several reasons, most importantly the big set of useful shortcuts, file management and the flawless playback when dealing with transcoded material. I was always told (by teachers at my university as well as when browsing forums on the web) that the generation loss during the import is negleable and that DNxHD is a codec that preserves a lot of image quality.
I work with a lot of DSLR footage and when comparing an original frame with a transcoded frame, the difference really isn’t too noticeable. But when I take a frame which is rather dark and add some color correction, the issues come to light. In the below picture the frame on top was AMA-linked, while the frame at the bottom was transcoded to DNxHD 185. The source material is from a Canon 5D Mark3, 1080p25, which matches the project settings. I put the same color correction effect (black/white and some curves) on both clips, than exportet both as DNxHD 120 and put them together in After Effects.
It’s needless to say that the above picture looks much more grisp and has far less issues with banding and compression artefacts. The transcoded clip looks washed out and you can see serious artefacting and banding (for example on the woman’s forehead). I’ve tried many different Avid Codecs, even 1:1 10bit MXF and DNxHD 365, but none looks anything as good as the original file when it comes to color correction.
I guess there is no solution to my problem except for switching to another software, but I wonder: If importing footage into Avid obviously reduces the possibilities of color correction, not to say that it decreases your over all image quality, how come nobody seems to care? Most companies I know use Avid.
Does this loss of quality bother any other Avid editor out there? How do you deal with it? Is an offline-online workflow via some other software like Davinci Resolve really the only way to get the most of your footage, while still using Avids great editings features? I mean, I’m not talking about some ARRi raw footage or something like that, just some simple h.264-compressed DSLR-footage.
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13 Replies
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I don’t think I’ve noticed quality this bad before. Then again, I don’t transcode to DNx185, and then to DNx120 on export. I either stick with DNxHD 185 throughout…exporting a QT in that codec…or output to tape. Wondering if the transcode to 185, and then again to 120 is the cause. Because that’s two levels of transcoding, where your AMA H.264 only had one at that point…H.264 to DNx120.
Why not export the transcoded footage SAME AS SOURCE…DNx185. And then the H.264 footage, export as DNx185…and then compare?
Shane
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No, the transcoding while export surely isn’t the issue. I just tried exporting both the transcoded frame and the AmA-linked one separately and it looks exactly the same. The difference is already visible inside Avid, the export doesn’t really change anything.
I’m not saying that the transcoding itself makes the footage look as horrible as in the picture. The difference only really becomes visible when color correction or other effects like keying are applied. Both frames that I posted where at some point transcoded to DNxHD, since I exported them from Avid, the only difference is that in the above picture it happened after making the picture black and white and modifying the luma curve.
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If you are on a Mac, you can also transcode to the Apple ProRes MXF. They are considered “native” for Avid and should have identical performance. I’d be curious to see if there is any quality difference.
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And yes. You can also use DaVinci Resolve to do your transcodes and see if that helps.
You probably have an Avid support contract if you own the software or are a subscriber. You should contact Avid support and let them know what you are seeing. This should not be happening.
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No, I’m on a PC so I guess importing ProRes won’t work. Still, I tried importing as XDCAM HD which looks somewhat different. More noisy, therefore less banding.
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Okay, apparently the issue goes away if I do not import the footage, but transcode the AMA-linked clips. Looks way better. What exactly is the difference between these two methods of ingest? They both convert the footage to DNxHD, don’t they?
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I am not sure whether this has anything to do with it but.. perhaps you are importing the footage with wrong colour space. For example importing 601/709 footage as RGB results in lower contrast. Try out different import options and let me know what happens.
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The color levels also aren’t the issue. It’s DSLR footage, import settings are RGB. If I select Rec709 when importing, the blacks are crushed but besides that the image looks just as bad, with heavy blocking. Transcoding via AMA is also a lot faster. Retranscoding my whole footage wasn’t really a big deal.
There seems to be another difference between import and Ama-link-transcode:
The Image shows the RGB-Parade of a black to white gradient I created in AE. As you can see, importing changes the gamma, while transcoding keeps everything as is. The gradient is RGB, thus 0-255. Why is it that the AMA-linked clip is still displayed as 16-235?
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Avid’s workspace by default is 16-235, but if you import the footage correctly that won’t have an effect on footage. You can still export as RGB and everything will be fine.
So the conclusion is that it is better to AMA link and then transcode the footage?
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Wait….you were importing DSLR footage? Good grief…don’t do that. AMA link then transcode. Its more modern, accurate..and also faster.
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