Erroneous 4k (UHD) Output / Horizontal Lines. Bug?

Hi everyone,

I'm new to DR and love it for its awesome usability and features. However, I've encountered a weird thing (bug?), where 4k footage is encoded with some horizontal lines/disturbances that can best be described as "interlace(ish)".

My source material is CGI footage at 3840x2160p with 60 FPS (using an AVI container with JPEG compression). DR has no problems handling the material and the project imports nicely into the timeline. Settings for the timeline are set to 4kUHD, 60 FPS.

When I encode/export the final movie (render settings set to 4k UHD, 60 FPS) I get weird horizontal disturbances in the output material that simply do not exist in the source footage.

Source material (cut-out from a 4k shot):

1-1_src.jpg (245.86 KiB) Viewed 1616 times

DaVinci Resolve Output:

1-2_out.jpg (262.19 KiB) Viewed 1616 times

It looks like some weird form of adding an unwanted interlace to the original material. A zoom on the encoded shot seconds that impression.

Zoom on Output File:

2-2_out.jpg (241.79 KiB) Viewed 1616 times

I already put countless hours into finding out what's going on, but didn't find anything. Any idea where that strange "interlace-ish" effect might be coming from?

Thanks,
Tim Boyd

[Peter Chamberlain]

Do u see this if u render to dpx?

Hi Peter, thx for looking into this. I did a render to DPX (RGB, 10bits) but the visual result was the same. The images show that unwanted interlace effect. For comparison, here's a close up of the zoomed-in source and output material side by side:

Source:

2-1_src.jpg (230.85 KiB) Viewed 1575 times

DR output:

2-2_out.jpg (241.79 KiB) Viewed 1575 times

If you have more ideas what to try out, let me know. I did a search on the forum for a possilble solution and found this thread (but it doesn't offer a solution):

viewtopic.php?f=21&t=95561

As a sidenote: My source footage is processed fine with a competitor's product. However, as that product is inferior to DR in almost every other aspect, I would love to switch over to DR permanently. Or maybe there's something I messed up?

[Peter Chamberlain]

can u post a link to a source clip so someone can test

Sure. Here you go:
https://brandkontor.de/files/test_footage.zip

This is an excerpt from the full footage in 4k/60 FPS/JPEG/AVI. It's a 226 MB download (zipped).

I reproduced the effect with that very clip. So, you should be able to hopefully reproduce this.

My system:
- Win 10 pro, 10.0.19041 Build 19041
- Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
- 64 GB
- RTX 2080 (8 GB of VRAM)

[Peter Chamberlain]

hi sam, i see tearing in the source image, and when played in another editor i see artifacts too.

can u try rendering to a different format, not Photojpeg/AVI

i see tearing in the source image, and when played in another editor i see artifacts too.

Yes, there are some artefacts from the PhotoJPEG compression. These are not my concern as I can control them in the source material's compression settings.

What looks so erroneous to me, are those repeating, horizontal interlace-ish break lines in the image.

About your screenshot: Are you saying this is a source screenshot? Because I can't detect these horizontal interlace-ish lines in the source material.

Here's a zoom shot of the same frame (pretty much) taken in VLC, playing the source material in native 4k screen resolution:

focus.jpg (90.52 KiB) Viewed 1513 times

Are you saying it's already in the source footage somehow?

can u try rendering to a different format, not Photojpeg/AVI

The render is an output from Unreal Engine 4. To my understanding, what the output does, is, take 4k JPEGs and throw them into an AVI container.

Anyway, I can render to PNG, BMP, JPG etc. single frames.

Do you want me to try that in the course of testing and finding out what's wrong on your end? Or are you suggesting this as a work-around to avoid the distorted output?

Best regards,
Tim

What looks so erroneous to me, are those repeating, horizontal interlace-ish break lines in the image.

Mediainfo app shows that the video is interlaced. I saw the interlace effect in Resolve too. That can be fixed by going to Clip attributes and Enable Deinterlace. And you should probably check the export settings in UE too.

VLC might deinterlace automatically if it detects interlaced footage.

Many players de-interlace automatically and cover the problem up.
If the clips are flagged erroneously, deactivate that flag with any of the free tools. If it is interlaced, get 17 Studio or use QTGMC.

Hi Timo, thanks for adding to this discussion...

Mediainfo app shows that the video is interlaced.

I didn't know MediaInfo. What a great little tool. Thanks for sharing this little gem!

And yes, you're right, that tool says "interlaced". However, this keeps getting more weird and weird, as A) UE4 doesn't support interlaced export and B) Resolve says it's progressive (scroll down a bit in this screenshot):

Unbenannt-1.jpg (394.75 KiB) Viewed 1497 times

Also, the editor I came from (Magix Video Pro X... yea, I know ) treated the source as progressive and its output didn't have these nasty interlace lines neither.

VLC might deinterlace automatically if it detects interlaced footage.

Yea, but then it would de-interlace Resolve's output too. I can see the interlace distortion in Resolve's output, but not in the source material.

That can be fixed by going to Clip attributes and Enable Deinterlace.

Since I'm still evaluating Resolve, I'm on the free version. It does not support that feature.

You should probably check the export settings in UE too.

UE4 does not offer interlaced export. I use default export settings (there aren't that many options anyway). So, if I run into this, pretty much everybody will.

Anyway, apart from the trouble with my footage and Resolve, there's this clear issue of Resolve "thinking" it's progressive and MediaInfo saying it's Interlaced. One of them is clearly wrong.

[Peter Chamberlain]

try jpeg single frames first

Oh, I didn't know deinterlace was a Studio only feature.

If it's falsely tagged as interlaced you can probably change it with ffmpeg, another small but powerful tool

Resolve can read image sequences as a single clip so you could just export a folder full of frames like Peter suggested and bring it in.

Try rewrapping your source footage from AVI to mov using ffmpeg’s copy function.

I didn't want to re-process the existing AVI/PhotoJPEG footage, as I expected the quality to degrade to an unacceptable point (the JPEG compression was already hard to swallow). I.e. I didn't try to de-interlace the existing footage.

I changed my workflow to exporting to single frames (lossless/PNG) and convert the frames to a ProRes sequence. The file is about twice the size of the PhotoJPEG AVIs i used to work with, but tons better in terms of quality.

Importing the ProRes clips to Resolve eliminated my problem with the strange interlace lines. It remains a mystery, why Resolve outputs the original PhotoJPEG/AVI as an interlaced video. Unreal Engine is not able to export interlaced footage, so my source material surely was progressive (and is treated as such by other video editors).

Anyway, I would like to thank everyone commenting on this. Besides this minor issue I find Resolve a very capable and professional editor. And the community here seems friendly, helpful and engaged. Awesome! I'm going to permanently switch to Resolve. Thanks!!

Best regards,
Tim

P.S.: I edited the title of the thread silghtly, to better reflect my issue. Maybe other Unreal Engine 4 users experiencing the same phenomenon will find this thread and add to it in the future.

Rewrapping from AVI to mov does not degrade the picture. It just puts the same data from one container to another.

Rewrapping from AVI to mov does not degrade the picture. It just puts the same data from one container to another.

Yes, I know. That's why I specifically said that I didn't de-interlace it.

I didn't want to try this, because even if it would work, it wouldn't be a solution that is simplier than exporting to single frames from UE4 and then converting to ProRes (i.e. it would also be a two-step process, which I'm stuck with now anyway, but got rid of the PhotoJPEG compression as a little bonus).

However, out of curiosity: Why do you think that a MOV container handles better with Resolve than an AVI container?