Teams: #FightCorona – In The Meeting: Playing video with audio

I have to deliver a course tomorrow. I also need to play videos that would be worthwhile for the learners since many in the class learn visually. I need the other participants to be able to hear the audio on those videos for the full experience. Up until last year, that wasn't possible in Teams, but there was a small feature that was introduced that meant that video with audio could now be used in meetings. This works whether the video is in a site such as YouTube, or embedded in a PowerPoint