External Display - Freezes when screen off

I use my iPad with a USB C hub that has HDMI out to a large monitor.
the iPad works fine as a “Cloned” display normally.
I do this so that i can also use a USB DAC and my good headphones, since the Apple TV has no USB support.

When i use a video player app such as Infuse, the video only plays via the external display though, so i guess something is programmed so that when full screen video is play, it only uses the external display for the video, and leaves the player controls, and background image etc on the ipad display.

I notice that I have to leave the iPad screen on in order for the video to play on the external display.
If i lock the ipad (to turn off its display) the image freezes on the external display while the audio continues to play in the background. I can turn on the ipad display by tapping it or press the power button, and it shows its lock screen with the media control widget thing showing, the video on teh external display continues, but as soon as the ipad display turns off again, external display freezes again.

Is there a setting or way to fix this so that I can have the ipad display off and use just the external display for playback?

Concerned about display burn in leaving it on with static text display for ~2hrs if i watching a movie or something. I have been setting the display to min brightness, but still a concern to me.

Any input?