Not sure if this helps but what I have done in one of my projects is to have a background title image displayed that I designed in Photoshop that has a keyhole with a transparent background.
Behind the image a series of pictures is displayed that move around and change.
Maybe you could draw a transparent circle the size of the speaker cutout and display that on a monitor placed behind the cutout.
The only problem is that the edges of the video footage will be missing but if you only want to display graphics then you can set where they appear within the circle by setting your coordinates.
A circular monitor would be great I agree.
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