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Creating HDR output using 444 Colour Sampling and BT2020 Gamut

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#1 GBlack
Hi,

I hope there is a way to tweak the output metadata a bit from LRTimelapse. When I create HDR output using LRTimelapse 444 Colour Sampling and BT2020 Gamut from 14 bit D800 source images, the output movie appears to be created correctly, but when imported into Final Cut Pro it considers the clip to be Standard 709. If I open the file in Compressor 1st, it indicates it is "709† implied" but lets you override this, which I do, specifying 2020 PQ. Exporting this to a temporary file with ProRes 4444 XQ allows me to open this intermediary file in FCP as 2020. Subsequent project output to either iTunes or Vimeo via Compressor using the "Apple Devices 4K (HEVC 10-bit) as the codec" gives me true HDR output (on a LG OLED TV).

Just wondering if there is a bit of metadata missing from the FFMpeg video output in LRTimelapse that would allow for the correct Gamut?

Thanks
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#2 gwegner
Apple seems to be a bit picky and individual sometimes in interpreting metadata. Unfortunatley I have no Final Cut and only a weak Mac to build new LRT releases, so I can't test. Maybe you could find out which setting FCP needs to recognize the files correctly, then I could try to add it.
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#3 GBlack
Thanks Gunther. I'm a little lost in regards to how the ffmpeg command is issued.
I see the following in the log file:
[2018-11-25 18:22:23] DEBUG: Stream #0:0: Video: prores (prores_ks) (ap4h / 0x68347061), yuv444p10le(pc, bt2020nc/bt2020/bt2020-10), 4096x2304 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 29.97 fps, 11988 tbn, 29.97 tbc
[2018-11-25 18:22:23] DEBUG: Metadata:
[2018-11-25 18:22:23] DEBUG: encoder : Lavc58.22.101 prores_ks
[2018-11-25 18:29:05] DEBUG: video:2410494kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000110%

FFMpeg docs indicate that the following are the probes_ks options:
---------------
9.15.1 Private Options for prores-ks

profile integer
‘proxy’
‘lt’
‘standard’
‘hq’
‘4444’
‘4444xq’

quant_mat integer
‘auto’
‘default’
‘proxy’
‘lt’
‘standard’
‘hq’
If set to auto, the matrix matching the profile will be picked. If not set, the matrix providing the highest quality, default, will be picked.

bits_per_mb integer
How many bits to allot for coding one macroblock. Different profiles use between 200 and 2400 bits per macroblock, the maximum is 8000.

mbs_per_slice integer
Number of macroblocks in each slice (1-8); the default value (8) should be good in almost all situations.

vendor string
Override the 4-byte vendor ID. A custom vendor ID like apl0 would claim the stream was produced by the Apple encoder.

alpha_bits integer
Specify number of bits for alpha component. Possible values are 0, 8 and 16. Use 0 to disable alpha plane coding.
------------------

I would guess that both '4444xq' and 'hq' need to be set, but I can't tell if they are. Is there a way to see the exact invocation that LRTimelapse uses so I could test with the command line?
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#4 gwegner
I'll contact you via email.
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#5 GBlack
For my part, I've been unable to find a way to have ffmpeg create a Rec. 2020 file that Compressor/Final Cut Pro doesn't tag as Rec. 709 implied. As a work around, post processing by via compressor before importing into Final Cut Pro will allow you to create an intermediate file that both Compressor and Final Cut Pro recognize as wide gamut
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#6 gwegner
Thank you for looking into this. Let's hope either Apple or ffmpeg will fix the problem soon.
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