I run a small sport stream to one stream destination, and we have several camera inputs, as well as pre-recorded videos (stream intro, stream outro, video ads), along with commentator sound coming from an external mixer to the PC via USB.

How do I set up my commentator sound audio input, to only send the commentator voice to the livestream when the camera inputs are in program, not the pre-recorded footage inputs?

I have tried several different setting combinations, and for some reason the commentator sound is sent to the livestream when ALL video inputs are played.

Is it not possible to do it without setting triggers or shortcuts up? My only concern with doing it this way, is if we were to do some odd number of transitions in/out we may fall out of sync based on how the trigger/shortcut logic is set up.

Would it work if I added audio input 1 (commentators) as a layer to the video input 1 (main camera), video input 2 (second camera), and NOT as a layer on the pre-recorded videos?

And then set the audio input 1 to global mute so as its own input, it doesn't do anything?

Yes it will work the way you say,if in the audio input (commentators) you tick "Automatically mix audio"