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BlackMagic Decklink Alpha Key output

Posted: Fri Nov 16, 2018 13:33
by erzyk
Hi,
I would like to ask if it is possible and how to output a full broadcast feed from Resolume over one BlackMagic DeckLink card. The thing is that all the newer cards supports RGBA or YUVA internal buffer inputs and outputs them on two SDI links: Out A is Fill and Out B is Key (only alpha channel).
I found methods in this forum telling to create a separate output with "Is Key" option, but this makes it impossible to use one card instead of two separate cards or a Duo card.

Is it feasible to use the full features of a BMD card and make use of the A and B outputs on newer cards for Key+Fill outputs? This would additionally avoid any delay between Key and Alpha.

Thanks in adevance

Re: BlackMagic Decklink Alpha Key output

Posted: Mon Nov 19, 2018 15:51
by Joris
So these cards don't have two assignable outs, but are hardwire to send out the key on a fixed second SDI port? Do you have a link to one of these cards?

Re: BlackMagic Decklink Alpha Key output

Posted: Mon Nov 19, 2018 17:19
by Oaktown
Currently the following Blackmagic capture devices support Key/Fill output:
  • Decklink 4K Extreme / Extreme 12G / Pro
  • Decklink Duo 2 / Quad 2 (see additional configuration steps below)
  • UltraStudio 4K / 4K Extreme / 4K Extreme 3 / HD Mini
The Decklink cards can be used for generating fill and key output but I don't believe any Blackmagic Decklink card supports RGBA/YUVA on either input/output side.

As far as I know, the 4:4:4:4 support is on UltraStudio hardware for file playback only.

Re: BlackMagic Decklink Alpha Key output

Posted: Fri Dec 14, 2018 14:43
by erzyk
@Joris - The newer Decklinks can output Fill/Key over 2 SDIs. The hardware is taking RGBA or YUVA input buffers and is splitting it into 2 SDI streams - one fill and one key for external keying/compositioning.

@Oaktown - now I have no access to my Resloume PC to test it, but do you mean that doing a screen output to one of the mentioned BMD cards will automatically generate two SDI (key + fill) streams without checking the "is key" option?

Re: BlackMagic Decklink Alpha Key output

Posted: Fri Dec 14, 2018 17:41
by Oaktown
@Oaktown - now I have no access to my Resloume PC to test it, but do you mean that doing a screen output to one of the mentioned BMD cards will automatically generate two SDI (key + fill) streams without checking the "is key" option?
Correct but in order for the blackmagic card to generate the key, you need to be able to output a signal with alpha (straight or premultiplied).

Re: BlackMagic Decklink Alpha Key output

Posted: Sun Oct 06, 2019 23:25
by Isse
The UltraStudio 4K is found by Resolume as a single device, you can not dedicate SDI A as one monitor and SDI B as another and due to this it won't work. I've spent days trying to figure this out and my findings are:

The US4K as 1 monitor out with 2 slices and one of which has "is Key" enabled in advanced on the output tab of one of the slices. Here is the thing, this look correct in Resolume as you have the bottom slice as alpha and the top slice as the viewable Fill but it still goes out on 1 output. There is no config available to split the 2 chanels over the 2 SDI outputs and as the signal goes out equal summed and ready, Key & Fill don't work as it should. Premultiplied, straight doesn't matter as far as I know.

I used both my BMD Mini Monitor and that worked with perfect result as I could config them as 2 outputs where I set one as the "is Key" which I summed in the switch but there was sync issues. When I did the same with 2 US4K units and synced then on ref input is worked like a charm. But still thats just bloody anoying to use 2 US4K for a simple task like that.

So basically the Resolume team have to add the feature to set up SDI output on units like the Ultrastudio rack decks if this is to be done by a single unit :-(

Re: BlackMagic Decklink Alpha Key output

Posted: Thu Oct 17, 2019 10:42
by Zoltán
+1

Re: BlackMagic Decklink Alpha Key output

Posted: Sat Oct 19, 2019 13:19
by chq
So is it meanwhile possible, to feed two (or four :o ) HD-SDI-outputs with different content?

Greetz Chris

Re: BlackMagic Decklink Alpha Key output

Posted: Mon Oct 21, 2019 11:36
by Zoltán
chq wrote:
Sat Oct 19, 2019 13:19
So is it meanwhile possible, to feed two (or four :o ) HD-SDI-outputs with different content?
Greetz Chris
With a 2 or 4 channel card, that would be easy: https://resolume.com/support/en/screens#playback-cards

With a 1 channel card that can send a 4 K signal on 4x SDI connections, you might be able to arrange your output slices to 4x1080p on the 4k canvas, and use the SDI signals separately.

Re: BlackMagic Decklink Alpha Key output

Posted: Mon May 25, 2020 19:12
by erzyk
Hi!

Some time ago we got the new version 7 of Arena. Are there any news about Alpha support with DeckLink cards from BlackMagic?
Most of live video software like vMix, CasparCG are perfectly supporting that feature.

Avoiding misunderstanding, it is not about getting a separate output with "Key Only" slice because this is not the correct way (unless some have enough resources and genlocks them correctly). It is about telling DeckLink to use the alpha channel directly from Resolume and handle it hardware wise (alpha will be present on a separate SDI link - the B link).

What is interesting, this feature is perfectly supported using NewTek NDI - the output is sent with full Alpha information.

Is it foreseen to add this feature to a professional video interface like DeckLink?