12bit UHD SDI capture is broken

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alatteri

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12bit UHD SDI capture is broken

PostFri Sep 23, 2022 1:23 am

Hello,

I've been trying to figure this out with the UltraGrid guys. When capturing a 12bit RGB444 UHD SDI input signal, the colors are all crazy. When SDI output is 10bit RGB444 UHD, capture is fine. See attached screen shots.

I've tested capture with UltraGrid, FFMPEG and even MediaExpress (Ubuntu). I've tested outputs from both Flame and Resolve (RockyLinux). Always the same results.

2K DCI 12bit RGB444 is fine though, the issue is only UHD.

I've tried several different decklinks, from UltraStudio 4K Mini, Decklink 8K Pro, DeckLink 4K Extreme 12G.

Settings in Resolve

IMG_0654.jpeg
IMG_0654.jpeg (330.21 KiB) Viewed 2090 times


IMG_0653.jpeg
IMG_0653.jpeg (147.69 KiB) Viewed 2090 times


IMG_0652.jpeg
IMG_0652.jpeg (214.58 KiB) Viewed 2090 times
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alatteri

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Re: 12bit UHD SDI capture is broken

PostFri Sep 23, 2022 10:31 pm

See this video, shows it all very clearly.

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alatteri

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Re: 12bit UHD SDI capture is broken

PostWed Sep 28, 2022 2:12 pm

This has now been reproduced by BMD support.
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Steve Fishwick

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Re: 12bit UHD SDI capture is broken

PostSun Oct 16, 2022 9:54 am

Are you sure SDI, even 12G, is capable of UHD 12 bit 4:4:4 bandwidth? I know HD is possible at that sampling. HDMI 2.0+ is though. For example HDMI 2.1 has a bandwidth of 48 Gbit/s, whereas 12G SDI has 12 GBit/s. The specs on my US Mini 4K say 4:4:4 and 4:2:2 SDI but not if at all resolutions. The crazy colours are consistent with 4:4:4 over 4:2:2. My reference monitor does the same with SDI, where it is only capable of 10bit 4:2:2 input, but HDMI is fine up 12bit 4:4:4.
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Jack Fairley

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Re: 12bit UHD SDI capture is broken

PostThu Oct 20, 2022 9:09 pm

Yes, 12-bit RGB 4:4:4 is part of the standard up to 30p. Should definitely be working as the OP has configured it.
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Steve Fishwick

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Re: 12bit UHD SDI capture is broken

PostWed Oct 26, 2022 4:47 am

BMD specs for the Extreme but not the US Mini 4K (he is using in the video) products specifies "2 x 12Gb/s SD/HD/2K/4K. Supports single/dual link 4:2:2/4:4:4. 2D/3D switchable." Which suggests dual link would be necessary for 12bit UHD 4:4:4, in the same way that HDCAM SR required dual link for 4:4:4, back in the day - the extra 0:2:2 carried the RGB, as it were.

The OPs screengrab shows single link and the result they are getting is consistent with losing the extra 0:2:2 component when a signal is really dual link SDI, high bandwidth RGB. I'm not saying you are wrong and he shows 10bit 4:4:4 as possible, but it seems like this is happening, at least for 12bit. So have you actually carried such a signal over single link?

Furthermore, in his video he says there is no way to get full range, as opposed to legal levels, in Flame with 10bit, therefore he needs 12bit. I'm not sure why this should be since bit depth and legal/full levels should have nothing to do with each other and the BMD SDK should be irrelevant when capturing to say DNxHR 10bit. What it shows to me is he has found the bandwidth limit for single link (the limit of the specific hardware shown too), which again has nothing to do with full/video levels.

Finally I might add that Ultragrid have "Dual-link transmission mode (sending via two different routes to achieve larger bandwidth)" in their specs and I would suggest he might try that for the 12bit UHD 4:4:4, if it's absolutely essential. Alternatively just declick 4:4:4 in Resolve output settings and you will have a 12bit 4:2:2 UHD single link signal that Flame can then use at full video levels. There most likely is a very specific reason that such a huge bandwidth is necessary but I've never heard of it for either live broadcast or streaming.

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