Decklink onboard hardware keying


A single Decklink channel CAN key over a live input without capturing into the PC. Live video to input > key overlay from application > Live video to output. This option can be demonstrated by the livekey utility that comes with decklink card, or in products such as Titlebox. Thus you can overlay graphics on a live video feed without capturing on one decklink channel, keying in software using CCG, and outputting to a second decklink channel.

Is there any way to use this feature of the decklink series with CasparCG, I only seem to be able to configure the damn thing to suck in video as a producer and output it as a consumer. It seems daft when the hardware is capable of doing a hardware ‘live’ key, that the CPU has to composite the production. The other beauty of using the Decklink hardware key you don’t get any latency on through the signal path.


Look at this post


Yep, started there - even using a declink duo, I just don’t get the ‘passthrough’ from the live input - all I get is the graphics. Its like there is no incoming signal (but there is as signal as can confirm with media express).

Very odd…


I never tried it wirh a Duo 2, only with the Extreme. But I would try the following: In Control Panel set the channels to be 4x single (no fill & key). Then in Caspar‘s config set keying mode to internal. That should probably do the trick.


What @didikunz said + if you can have the setup you want in LiveKey but not in CasparCG: do try with a newer CasparCG release. These bidirectional cards sometimes require some additional setup that wasn’t supported by older versions.

Also: when setting up the 2 channel mode in the Decklink setting (so two of the virtual cards getting two connectors, and two of them having no connectors) and configuring with the “internal” keyer option in CasparCG - check if there is some signal output on the connector that is supposed to be the signal input. That could point you in the direction of a solution.


I am actually using the original Decklink Duo not the Duo 2, so shouldn’t have any issues with the bi-directional issues.

The overall issue is that I have 16 x Xeon 2.6Ghz, Quad Core, Hyper-threaded Servers with NVIDIA Quadro M2000 cards currently all running SD 720x576 FHA. These servers didn’t quiet have enough ‘grunt’ to handle 1080i50. I got rid of my screen consumer, and CPU usage dropped to below 50% when running in 1080i50, so this is absolutely fine. Fortunately these are dual CPU motherboards, and because of the age of them I can upgrade them with a matched pair of CPU’s for under $150 (Ebay), and give them an extra 8Gb Registered DDR3. I can also upgrade the GPU’s which may help a little, but Caspar dosen’t seem to over use the existing GPU’s (< 50%).

It strikes me that if I can get the final ‘composite’ between all my final CasparCG graphics layer, and my live input performed by the hardware (as I know it can do) i would save a few CPU cycles and improve general performance (and wipe out the latency of the live signal introduced by latency).

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It will not work with the old Duo, as it does not have a hardware keyer.


the Duo 2 has a HD hardware keyer.
and you can even use Decklink SDI 4k to ad graphics to a HDSDI signal. (without the use of a mixer and audio loops to output)
You have to check the Black Magic settings for the card, there some output options that enable keying.


AFAIK only in SD.


No also in HD, I have just done this a few weeks ago with the newest cards.
Black Magic is not clear with information which card has a HD keyer.
Sometimes there are limitations with getting a Fill and Key out in HD.
I have used a Decklink SDI 4k to create a logo/ticker inserter.
I’m only using SDI in and out to loop the signal through the card.
I has nearly no delay (maybe 1 line)


That’s the non 4k version, SDI 4k can key internally in HD.