Issues with internal keying on a new Decklink 4K 12G extreme

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  • Joined: Tue Aug 07, 2018 2:15 pm
  • Real Name: Peter McEvoy

Issues with internal keying on a new Decklink 4K 12G extreme

PostTue Aug 07, 2018 2:37 pm

we have just acquired a new Decklink 4K 12G extreme card and have managed to set it up. It can capture input via HDMI, both from a computer (10bitRGB) and a camera (8bitYUV) both @ 1080p50 and 1080p25.

Now, the card will be used to help with compositing graphics over the live video feed, ideally with low latency. As I understand it internal keying, which this card has, can help with making it fast. However, I can not seem to get keying to work.

I have tried the following:
With output HDMI from the Decklink card going to a separate screen.
  1. Using the supplied LiveKey program. I pick an image to key ( ... QBylIQZ7tU) and select the correct video format to what my input is sending (1080p50), set keying to internal and start to slide around with the keying slider. On the output screen I only see a static image of the key image, no feed from the camera.
  2. From the SDK GDIKeyer Sample, using both the precompiled and building my own (with keyer->Enable(true)). The program runs and detects the correct screen resolution, and then starts ramping up the key amount. However, again, on the output screen, only a static image of a test pattern is shown, no feed from the camera.
This is on a new and clean machine running windows 10. It has the decklink drivers installed and not much else.

Am I misinterpreting something, does the internal keyer not work as I imagined?
Does it perhaps not work when using the two HDMIs as both input and output?

Thank you very much for any help or pointers regarding this.

Kind Regards

Dave Del Vecchio

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Re: Issues with internal keying on a new Decklink 4K 12G ext

PostWed Aug 08, 2018 11:45 pm

I believe this should work, I have done internal keying on a DeckLink 4K Extreme 12G at other resolutions and frame rates.

Here are a few things you can check:

1. Only one of the video inputs on the DeckLink 4K Extreme is active at any time, so you have to set the input source to be HDMI in the Desktop Video Utility for the HDMI input to be active (otherwise the SDI input is used).

2. When using internal keying, the input resolution and frame rate has to exactly match the resolution and frame rate that the keyer is set to use. With HDMI inputs in particular (due to the EDID detection), often the actual HDMI signal format is different from what may be set at the video source (this is especially a problem with cameras which will often output 1080i even if set to record in 1080p).

3. You might want to try using Media Express to capture video from the same input source to make sure that the video is getting into the card and that the input signal is the resolution and frame rate you expect (you'll have to close LiveKey when capturing via Media Express).

4. Make sure that the image you are using for keying actually has transparency in it (otherwise it would overlay the entire video). Maybe try a different file format (PNG) or different save settings for the image file to see if that makes a difference.

5. If you can, try sending the input video through an HDMI to SDI converter and into the SDI inputs on the DeckLink card to see if keying works in that configuration.


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  • Joined: Tue Aug 07, 2018 2:15 pm
  • Real Name: Peter McEvoy

Re: Issues with internal keying on a new Decklink 4K 12G ext

PostThu Aug 16, 2018 1:12 pm

Thank you for your tips Dave!

I did give it another good try and tried to keep your points in mind.
I did get video output when using ntsc as the format in LiveKey, even though I was sending 1080p in.
However, it seemed to only work intermittently.

In case anyone else is looking for information about this, I also sent this question to Blackmagic support. They did a test with my configuration (HDMI in and out) and could confirm that the internal keying does not seem to working in that case. Using an SDI output and HDMI did however work. So the quick workaround for my setup is to get an SDI to HDMI converter.

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