Key & fill out of sync on decklink 8k pro when using external_separate_device

sarksim · February 15, 2022, 9:52am

Yeah, so I’ve noticed that sometimes my key & fill go out of sync. Haven’t been able to pinpoint what exactly causes this. I’m using a decklink 8k pro set up as 4 separate devices and server 2.3.3. Config looks like this:

    <channels>

        <channel>
            <video-mode>1080p5000</video-mode>
            <consumers>
              <decklink>
                <device>1</device>
                <keyer>external_separate_device</keyer>
                <key-device>2</key-device>
                <embedded-audio>true</embedded-audio>
                <buffer-depth>3</buffer-depth>
              </decklink>
            </consumers>
        </channel>

        <channel>
            <video-mode>1080p5000</video-mode>
            <consumers>
              <decklink>
                <device>3</device>
                <embedded-audio>false</embedded-audio>
              </decklink>
            </consumers>
        </channel>

        <channel>
            <video-mode>1080p5000</video-mode>
            <consumers>
              <decklink>
                <device>4</device>
                <embedded-audio>false</embedded-audio>
              </decklink>
            </consumers>
        </channel>

    </channels>

Any ideas? Is it a caspar thing or a decklink thing? Should I be using a single device for key&fill to ensure sync? I’d like to have one key&fill pair and two discrete outputs and with the 8k decklink card that’s only possible when it’s configured as 4 devices afaik.

didikunz · February 15, 2022, 10:00am

I never configured an 8K card myself. But I am told, that it works the same as the Duo 2.

So actually you should be able to configure one channel as a fill & key in the control panel applet and leave two as using a single BNC each. Set device 1 keyer mode to external, get rid of the key-device line and move the device number of the two remaining channels as being 2 and 3 (instead of 3 and 4). That should do the trick.

Andrea · February 15, 2022, 10:18am

Hi Sarksim, didikunz is right, you need to go to “Desktop Video” and configure 1+3, 2+4, don’t bother if is in&out.
Then in the config file just leave only one of the two channels but with external keyer.
Here my config:

        <channel>
            <video-mode>1080i5000</video-mode>
            <consumers>
                <decklink>
                    <device>1</device>
                    <latency>normal</latency>
                    <keyer>external</keyer>
                    <key-only>false</key-only>
                    <buffer-depth>3</buffer-depth>
                </decklink>  
            </consumers>
        </channel>

in this way the key is generated internally by Decklink and is always in sync
if you need a second f+k just put device=2

tsipas · February 15, 2022, 12:42pm

Hi
I have both pro4k and 8k and doesnt managed to make it work like duo 2 Two scenarios working fill+key x2 or 4 fill. I tried only output mode. I speak for HD channels If you want 4k two sceanarios, 4k at BNC 1 or 4HD sync at 4 BNC

didikunz · February 15, 2022, 3:02pm

Do I understand you right: At 4K you need all 4 BNC to deliver a 4K? Or at least you only get one channel? What is the pro4K? A 4K SDI?

tsipas · February 15, 2022, 6:01pm

Pro4k is the previous model that replaced by pro8k I mean there are two ways to get 4k One from BNC at position 1 and the other to connect 4 BNC at outputs and combine a 4k signal through 4HD (like quad but synchro)

sarksim · February 15, 2022, 11:14pm

You’d think so, but no. With the 8k pro for some reason you can only configure 1, 2 or 4 devices to the card in desktop video app. I found some posts on the blackmagic forums and it looks like this was an issue already back in 2019.

I used to have the card configured like @Andrea mentioned, but that means I only get f&k + one output.

Andrea · February 15, 2022, 11:33pm

Now I’m trying to have one channel f+k and two separate i/o channels, with no much luck. Is this the mentioned issue with the 8k?

sarksim · February 16, 2022, 8:43am

Yes. I can’t find any info on why this is the case though.

didikunz · February 16, 2022, 10:02am

That is good to know. So it seems to be possible to have 2x fill & key. Do you know up to what resolution / frame rate that is possible?

Andrea · February 16, 2022, 10:20am

@didikunz Yep, it’s possible to have 2ch f+k, I can confirm that, it works fine. I only used at 1080i50 because I don’t have any 4k equipment at the moment.

@sarksim I forgot to mention, because it’s not really a solution, that you can use 4 channel and then put in sync fill-key.
You have to play with the buffer length,

<buffer-depth>3</buffer-depth>

it has the effect to delay the channel itself.
Of course is more a workaround than a solution, and also I just tried for few minutes so I don’t know if could change between reboot or if is stable and reliable.

sarksim · February 16, 2022, 10:40am

I’ve only done 1080p50 so far, but next week I can test how high it can be pushed.

sarksim · February 16, 2022, 10:46am

Thanks, but I don’t think that would solve the problem since key&fill are not always out of sync, in fact most of the time everything works ok. I contacted Blackmagic support to see if they can come up with a solution.

didikunz · February 16, 2022, 11:00am

Or just add a small one channel card for the second projector out.

tsipas · February 17, 2022, 10:29am

I think if you dont need 4k channel the best solution is DUO 2 you can do all the channels whatever you want and cheaper.
I believe is something with DesktopVideo software , when I bought my first pro4K I noticed that I can send 4K only with use of 4 BNC outputs and send the 1/4 of video and create the 4K output.
After 2-3 days with a newer DesktopVideo version I managed to send full 4k only from BNC number 1
But still there are only two configurations with pro4k or pro8k , 2 FILL+ KEY OR 4 FILL

sarksim · February 18, 2022, 5:44pm

Blackmagic support confirmed that it isn’t currently possible to mix dual-link and single link devices on a 8K Pro, but they didn’t say if it would be possible at some point in the future. They also said I should use a reference signal to sync the outputs, which is what I’m going to do.

bobby.dk · April 26, 2023, 10:04am

Hi @sarksim

Did you ever test resolutions higher than 1080P? Seems like the Decklink 8K Pro hardware supports 2x key + fill on 4k 60 4:2:2.

I would like to send two 4k 60 HTML5 transparant overlays into an BMD ATEM 4 M/E Constellation 4K, (vMix does appear to support this with the Decklink 8K Pro hardware though i’m anwaiting awnser from their support team to comfirm this).

@didikunz On the official wiki the Decklink 8K Pro is not supported on " Server: Supported Video Hardware" but from this conversation it appears that it is supported?

Another noob question you might be of help with, is key + fill the only way to acchive 4k transparanty on 12g SDI? New BMD 12g ATEM hardware appears to also support an alpha channel wich would make key + fill unnecessary?

didikunz · April 26, 2023, 10:15am

AFAIK it should work. I have never tried myself.

Key & fill is another way to do color and alpha. SDI is not able to transport an alpha channel beside the colors. So you need a separate cable for the alpha, called key.

Julusian · April 26, 2023, 10:24am

Really? The SDK docs say that the 8K is the one card that doesn’t need an external sync when recreating the K+F pairing in software.

This is something I have been looking at recently, as part of custom resolutions and getting multiple outputs in sync.
The implementation of external_separate_device is relying on there not being any drift in clocks, and for no frames to be dropped/skipped/repeated.
The SDK and these newer cards (8k pro, quad2, duo2) have some new functionality that allows for this kind of use case of pairing outputs and running them with a single clock which should avoid these drift issues.
Hopefully at some point this external_separate_device can be replaced with a better sync mode that will allow for grouping outputs to keep them in sync which will also solve the sync issues I was seeing with custom resolutions.

bobby.dk · April 26, 2023, 1:07pm

vMix support just came back with the following regarding the Decklink 8K Pro.

Unfortunately, the Decklink 8K Pro is configured a little differently internally than other Decklink cards and in our testing did not behave as expected for Key + Fill Output and so we do not recommend it for that and why it is not listed in our documentation for Key + Fill support

This concludes that in vMix the DeckLink 4K Extreme 12G is the only card that can output 4k 60 key + fill (1 channel) the Decklink 8K Pro is not supported.

This brings us back to my original question, is CasparCG/ Decklink 8K Pro capable of outputting 2 channels key + fill 2160 60hz (on a single Decklink card

@Julusian I just found the following (older) thread:Decklink 8k pro - #19 by Andrea
Here @Andrea states

I have a DeckLink 8k Pro fully functional, double channel fill+key
for me the trick was in the blackmagic settings: 1ºin+2ºout and 3ºin+4ºout
in this way the f+k are linked together and perfectly in sync
(external keyer)
I tried only in 1080@50i, I don’t have any way to test higher resolution at the moment

That might help with your sync issues?

Seems like no one has tried @Andrea’s working config file for two key and fills in 2160p/i5000
This is exavly what i would like to do, but i do not have the 8k card yet.