Stopping audio feedback when sharing a video in Zoom

Working on a trial in federal court right now, and assisting with the courtroom electronic presentation. When doing the a/v setup, I learned a valuable lesson about how to prevent feedback. I had my laptop connected to speakers and monitors with a VGA cable fed through a HDMI converter to my laptop and separate audio cable - VGA will not transmit an audio signal.

I needed to confirm that I would be able to share a PowerPoint presentation in a Zoom session with a witness testifying remotely. Initially, when I tried to play a video clip in the PowerPoint I got very loud feedback - sort of like someone banging an industrial metal drum. The IT staff for the court helped me to discover a solution to the problem.

The first step was to mute both the mic and video on Zoom.

You can still play audio through the Share Screen function even if your mic for Zoom is muted.

The next step was to adjust the audio mixer for Windows so that only the feed for the 'headphones' - the port where the audio line was connected - and the sound for PowerPoint was enabled. System sounds, sound for Zoom itself, and sounds for all other applications were all muted.

. . . scroll back and forward in the Volume mixer to find other applications you may need to mute.

Finally when sharing the PowerPoint in the Zoom session be sure to click the option to share sound and optimize video.