Color shift when encoding DNxHD QuickTime Video

[Yani Lathouris]

Hello

I have been tasked with developing the Editorial submission pipeline for an animated feature film project. Our studio is based on Windows 7 and the Editing team is using Avid Media Composer. We have decided to go with the "fast import" approach for bringing media into Avid. My tools take some frames and encode DNxHD QuickTime videos from them, then we write out an ALE document to assist with the batch importing of the delivery content. We call it the "fast import" approach because Avid only has to change the video container from MOV to MXF and it doesn't have to do any real encoding which is usually the time consuming part.

I have tried comparing DNxHD QuickTime videos encoded using FFmpeg, RVIO and Nuke. The color in each video is different but the only one that matches the video created by importing frames directly into the Avid is the video generated by Nuke. I have heard the color shift may be caused by the way the Apple QuickTime libraries manage color on the Windows platform, is this true? If so, how is Nuke able to produce the correct output? Also, is there any way I can produce the correct output using FFmpeg or RVIO?

[jagabo]

rec.709 vs rec.601? (color shift)
https://forum.videohelp.com/threads/329866-incorrect-collor-display-in-video-playback?p...=1#post2045830

PC vs rec matrices? (levels shift)
https://forum.videohelp.com/threads/340804-colorspace-conversation-elaboration?p=212150...=1#post2121505
https://forum.videohelp.com/threads/329866-incorrect-collor-display-in-video-playback?p...=1#post2045481

Yes, Quicktime on the PC is hopelessly screwed up. How are you comparing the output? Using media players is the least reliable method. The exact same video played in two instances of the same media player can look different because one can use Windows' Video Overlay and the other may use Windows GDI -- the two have different proc amp settings.

[smrpix]

Link the clips into Avid via AMA, then transcode to the resolution of your choice. It is faster than importing, maintains color levels and retains metadata.

[Yani Lathouris]

@ smrpix: I don't know much about the AMA workflow, It was considered when we first set-up editorial but we didn't end up going down that route for some reason. Perhaps it is still an option for this particular problem though. Can the AMA approach be automated? Or is it more of a user driven process? I have also looking into using Avid MetaFuze from the command line but couldn't manage to get it to export media at 25 fps.

@ jagabo: Very educational, thanks! I am not entirely sure how to get FFmpeg and RVIO to use the correct RGB/YUV conversion matrix. I know we were able to access options from the Apple QuickTime libraries via Nuke, ie. we were able to set the Output Color Space to rec709 along with other properties such as Resolution, Frame Rate and Bit Rate. Below is the RVIO command I used to convert the frames to video:

Note: The input image files are TIFFS in sRGB color space, the output video needs to be an Avid DNxHD QuickTime video, 1920x1080, 25 fps and 185mbps in rec709 color space.

rvio "c:\temp\input\image.@@@@.tiff" -codec AVdn -outres 1920 1080 outfps 25 -outdatarate 185000 -out709 -o "c:\temp\rvio_output.mov"

You will notice there is an argument -out709 which says it will convert output to rec709 color space. The video produced by this command does not match the videos created by Nuke and Avid. I also tried using the -insrgb argument which says it will convert input from sRGB to linear but that didn't solve the issue either. Also, here is the FFmpeg command I used:

ffmpeg -f image2 -r 25 -i "C:\temp\input\image.%04d.tiff" -s 1920x1080 -vcodec dnxhd -b:v 185M -r 25 -pix_fmt
yuv422p -mbd rd "c:\temp\output_video.mov"

Seeing as I am trying to create a video that matches the video created by Avid when importing an image sequence, I am using Avid Media Composer to compare all the results. There is also an option to use a 0-155 or 16-235 color range when importing media. I have tried importing my FFmpeg and RVIO videos using both color ranges without success.

Thanks for your answers!

Cheers

[poisondeathray]

You fail to describe the precise issue; "color shift" is pretty vague. It would be more informative if you posted some screenshots

If it is the wrong matrix from the tiff RGB=>YUV using Rec601, in ffmpeg or ffmbc you can use -vf colormatrix=bt601:bt709

DNxHD is a PITA to work with because of these issues, lack of consistency (levels and matrices) not only across platforms (PC, Mac) , but across different software on the same platform even

[jagabo]

Note: The input image files are TIFFS in sRGB color space, the output video needs to be an Avid DNxHD QuickTime video, 1920x1080, 25 fps and 185mbps in rec709 color space.

rvio "c:\temp\input\image.@@@@.tiff" -codec AVdn -outres 1920 1080 outfps 25 -outdatarate 185000 -out709 -o "c:\temp\rvio_output.mov"

You will notice there is an argument -out709 which says it will convert output to rec709 color space. The video produced by this command does not match the videos created by Nuke and Avid. I also tried using the -insrgb argument which says it will convert input from sRGB to linear but that didn't solve the issue either.

Did you try both -insrgb and -out709? If the program doesn't know the sources are sRGB it will not convert to rec.709 correctly.

[smrpix]

Didn't understand you were using TIFFs initially. But even so, why not just import the (numerically ordered) TIFFs directly into Avid as an image sequence to DNxHD 185?

when you import set "File Pixel to Video Mapping" to "601 SD or 709 HD (16-235)" to not touch the color space, or use one of the RGB settings to remap to studio swing.

You can modify the metadata in the bins, then hand off the bins and mxf files to whomever needs them down the line.

I think I'm still not really understanding what you're trying to do or why you're going outside of Avid to do things it does well.