H.264 to DNxHR 444 issue. Colors are not transcoded correctly (HDR project). Note: issue not solved yet

Question

I'm having an issue transcoding a H.264 UHD HDR file to a DNxHR file in a mxf container with FFmpeg. The issue is that both files don't look the same at all, the colors look washed out on the DNxHR video, and I tried to make the transcoding as lossless as possible (DNxHR 444 flavor). The original file is a movie I ripped a while ago, H.264, UHD, HDR, in a mkv container.

My goal: to create an almost lossless DNxHR file to use it as source file in Adobe Premiere Pro, and use another DNxHR file with less quality as proxy for editing. I wanted to do it that way and not use the original H.264 as the source file because it's out of sync with the proxy file (I mean, when I toggle the proxy icon on and off, you can tell that there's a short delay between them, which defeats all purposes for editing). My guess is that it may be because H.264 is compressed and DNxHR isn't, and since I edit making a lot of fast cuts, I need both the source file and the proxy file to be as synced as possible. When the source file and the proxy file are both DNxHR, no matter the flavor, they are perfectly synced. I don't want to go with Prores for the proxies, because the sync problem is a lot worse (several seconds of delay between files), maybe because it's a VBR codec and my original file and DNxHR are CBR (for the record, I always prefer CBR).

Well, the thing is that when I import the original H.264 file to Premiere Pro, use a DNxHR proxy, edit a little, and export it directly from the original file (H.264 10 bits, with all the settings required for HDR output enabled) the colors look as they should. When I do the same with the high quality DNxHR as source file, with the exact same export settings, the colors look washed out. The same with any DNxHR flavor.

Then I opened both files (original H.264 and high quality DNxHR transcoded from the H.264 one) with VLC, and I also can tell that the mxf file looks washed out and the H.264 file doesn't. So it's not an export issue on Premiere' side, it's something that has to do with the original transcoding.

I understand that DNxHR 444 is as lossless as you can get with that codec, preserving all the HDR required data, and I believe that the mfx container has some advantages over MOV, which is the other container that supports DNxHD/DNxHR. So I don't know what's happening really.

The command I used was:

ffmpeg -channel_layout 63 -i input.mkv -map 0:0 -c:v dnxhd -vf "scale=in_range=limited:out_range=full" -color_range 2 -profile:v dnxhr_444 -pix_fmt yuv444p10le -acodec pcm_s24le -ar 48000 -ac 6 -channel_layout 63 -map 0:2 -hide_banner output.mxf

Like I said, after the transcoding, both video files look a lot different from each other, color wise. And after using them in Premiere and exporting with the exact same settings, the output files suffer from the same difference.

Mediainfo shows the expected data for both files: - 10 bits, main 10, level 5, 4:2:0, CBR, BT.2020 for the original h.264 file. - 10 bits, 4:4:4, CBR for the DNxHR 444 file.

One thing I noticed in Mediainfo is that both have YUV as color space, but the DNxHR 444 video has an extra field that says ColorSpace_Original: RGB. Honestly, I don't know what that means, since the original is YUV. Color range is fine, from 0 to 1023 (and chroma range 1023). The other thing is that it says "limited" on the color range field of the H.264 file, but I've read that that could be a bug or missinterpretation of the file by Mediainfo.

Well, that's it, any help would be appreciated. I'd really like to edit with DNxHR 444 as source file and DNxHR LB for the proxies, so I can edit in a fast pace and without sync issues, but the color is just not acceptable. And I do understand that I'm adding an extra transcoding step (from original to DNxHR), but the sync issue between the original and the DNxHR proxies, even though it may be a delay of a fraction of a second, makes my workflow a lot harder since I'll have to export many times to see if the cuts are made exactly where I want them to be. Not ideal by any means. And Prores is not an option apparently, the sync issue is a lot worse. For me, it all comes down to being able to get a DNxHR 444 file that looks, well, as close to lossless as it can be, and that goal obviously involves the colors.

Thanks in advance.

PS: file size is not an issue for me, so having an entire UHD HDR movie transcoded to DNxHR 444 is not a problem.

PS2: I tried with a different chroma subsampling (like DNxHR HQX 10 bits, which is 4:2:2), same result. Haven´t tried with 8 bits yet, but I don't see the point since this is a HDR project.

UPDATE:

I tried to transcode from the H.264 source file to a DNxHR video file in a MXF container using Adobe Media Encoder instead of FFmpeg, and the colors are not transcoded correctly again, but this time they seem to be over saturated instead of washed out. Adobe Media Encoder doesn't give much room for tweaking, but I made sure to select 444 10 bits profile, same resolution (UHD), same frame rate and render with maximum quality and maximum bit depth. FFprobe output of the resulting file again shows BT709 as the color space (the same thing happens with the output file after transcoding using FFmpeg). Seems to be something not related to FFmpeg, apparently. Any ideas? It's like there's no way I can transcode and retain the colors correctly from H.264 to DNxHR, even using its most high quality flavor and correct command settings (at least they look ok to me). How can I post this so maybe developers or people with lots of experience here can give us a clue to what's happening? Thanks.

PS: More potentially useful info on the comments below.

EXTRA INFO:

1) FFprobe output of the MXF DNxHR file (this one is 4:2:2, the only difference with the command used compared to the one stated on the OP is -pix_fmt yuv444p10le being -pix_fmt yuv422p10le):

  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
[mxf @ 000001f4d17fbac0] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, mxf, from 'Interstellar_Master_DNxHR_444_UHD_422_PCM24_5.1.mxf':
  Metadata:
    operational_pattern_ul: 060e2b34.04010101.0d010201.01010900
    uid             : adab4424-2f25-4dc7-92ff-29bd000c0000
    generation_uid  : adab4424-2f25-4dc7-92ff-29bd000c0001
    company_name    : FFmpeg
    product_name    : OP1a Muxer
    product_version : 58.29.100
    product_uid     : adab4424-2f25-4dc7-92ff-29bd000c0002
    material_package_umid: 0x060A2B340101010501010D001393EE79529471348D93EE7900529471348D9300
    timecode        : 00:00:00:00
  Duration: 02:49:03.97, start: 0.000000, bitrate: 1404833 kb/s
    Stream #0:0: Video: dnxhd (DNXHR 444), yuv444p10le(bt709/unknown/unknown, progressive), 3840x2160, SAR 1:1 DAR 16:9, 23.98 tbr, 23.98 tbn, 23.98 tbc
    Metadata:
      file_package_umid: 0x060A2B340101010501010D001393EE79529471348D93EE7900529471348D9301
    Stream #0:1: Audio: pcm_s24le, 48000 Hz, 6 channels, s32 (24 bit), 6912 kb/s
    Metadata:
      file_package_umid: 0x060A2B340101010501010D001393EE79529471348D93EE7900529471348D9301

2) FFprobe output of the MP4 H.264 source file (this one is 4:2:0, 10 bits, HDR):

    Stream #0:0(eng): Video: hevc (Main 10) (hev1 / 0x31766568), yuv420p10le(tv, bt2020nc/bt2020/smpte2084), 3840x2160 [SAR 1:1 DAR 16:9], 15584 kb/s, 23.98 fps, 23.98 tbr, 16k tbn, 23.98 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(eng): Audio: ac3 (ac-3 / 0x332D6361), 48000 Hz, 5.1(side), fltp, 640 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
    Side data:
      audio service type: main
    Stream #0:2(eng): Data: bin_data (text / 0x74786574)
    Metadata:
      handler_name    : SubtitleHandler
Unsupported codec with id 100359 for input stream 2

Answer 1

It would help if you could post the output of ffprobe on the H264 file? There's a few things that could be causing this, most of which we can figure out by seeing what type the input file is.

The H.264 is likely 4:2:0, and you're upsampling to 4:4:4 (-pix_fmt yuv444p10le) or 4:2:2 ("PS2"). For all practical intents and purposes, conversions are never a good thing for quality, so if the file is 4:2:0, keep the data in 4:2:0 forever after. You won't get the information back, but the conversion will introduce further quality loss. The same is true for your conversion from limited to full range (scale=in_range=limited:out_range=full).

Since DNXHD does not actually support 4:2:0, you have various options. One simple one is to use intra-only H.264. The issue with sync is with inter frames, intra is fine, so use intra-only (-g 0 or -intra).