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I am looking for something uncommon: A device that would allow to merge the image coming from 2 outputs (HDMI, DVI, VGA or any other type of image output) into one final image displayed onscreen. The outputs can be of the same type (e.g. 2 HDMIs) or different, anything that works would do. In case that isn't clear, here is a simple schema:

Image merging

It could work in different ways, for example with a system of priority (e.g. output 1 write its image and the output 2 overwrite non transparent pixels), less ideally by addition (e.g. if there is a red pixel 0xFF0000 on output 1 and a green pixel 0x00FF00 at the same position on output 2, the pixel becomes yellow 0xFFFF00), or any other method.

I checked the available devices and none of them seem to be able to do this. Another solution would be to have a separate computer, able to capture video input from the outputs of the main computer, does the merging operation and send the image to the screen for display. The video capture device I could find only have one input and one output to record then display the image (these are generally game streaming devices) and wouldn't allow me to merge the images in real time. I could not find a video capture card for computer with multiple inputs that I could use to merge the images either.

If you have any idea on how to accomplish this, please let me know.

Thank you and have a good one.

Pierre Ciholas
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2 Answers2

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In the broadcast industry we call what you are looking for a video mixer. Those that TV stations use are incredibly expensive but guarantee stable 24/7 operations. The signals for those guys are not HDMI but SDI. So when capturing from HDMI they just get a HDMI to SDI converter.

The base problem that can only be solved by investing money is that you need some device that allows you hdmi recording. There are many manufacturers out there, a cheap one i can recommend is blackmagic.

On their website you find products like decklink cards that allow HDMI over PCIe capturing, you could grab 2 of such decklink cards. Or you go for their external cards using USB3 or Thunderbolt solutions. But be prepared for unstable operations on USB3. Uncompressed video signal is really a lot of data, USB3 is just not ment for 24/7 operations. External connections in general are not good for those huge amounts of data in 24/7 operations.

When you have both signals running into one box, you need to choose for the software of interest. If you are a c++ guy, you can directly go with the SDK from Blackmagic. In any other case, you should look out for software already supporting the capture card of interest. E.g. ffmpeg seems to support PCIe decklink cards. My favourite SDK for this kind of task is the MFormats SDK from medialooks, it costs some coins but it massively speeds up and eases development for such tasks.

Regarding transparency i would have much more but i guess what i wrote is enough.

I know i shouldnt have written an answer but downvoted and commented instead as this is not development related at all but a comment would not allow me to put all the infos in here.

Harry
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  • Thank you Harry, I found out the Black Magic cards and indeed that can be a solution. I am going to look for cheaper solutions and if I don't find anything else I will just go with that. Thanks again. – Pierre Ciholas Mar 31 '18 at 06:51
  • I forgot to ask, are you sure you need to capture the hdmi signal? A cost-free way to solve this would be to do screen capturing and stream the signal into network. https://trac.ffmpeg.org/wiki/Capture/Desktop and https://trac.ffmpeg.org/wiki/StreamingGuide could help – Harry Mar 31 '18 at 07:31
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It looks like you’re looking for a multiviewer. Here are some examples

  • Avenview 4x2 HDMI 2.0a UHD 4K60 Quad Multiviewer with USB Video Capture
  • Expert Connect 4 Ports Quad HDMI KVM Multi-Viewer/Screen Divider/Switch

These are not the only ones (by far) and if you do a search for a “multiviewer” more should pop up.

Marc
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