Using Display Port or HDMI Port as Video / Audio Source in Linux

We have an Intel NUC running Ubuntu 16.04, that is being used to test an A/V device.

The A/V device needs to receive a static image & audio sine wave on it's input port (the input port is an HDMI port).

Rather than using a signal generator, we are hoping to leverage one of the NUC's HDMI or Display Ports to display the static image (test pattern jpeg) and a sine wave tone.

Ideally, when connecting the NUC's port to the A/V device, it would be nice if the NUC did not think it had a second monitor attached, and we would just be able to display the image / tone like a signal generator would.

Has anyone encounters a task like this?

Any suggestions are greatly appreciated!

Thank you,

Dan.