Iframe confusion with playercard


I’ll start off by saying, I know basically nothing about iframes, and yes, I should read up on them.

That said, I’m trying to create a player card that displays a still photo, and when clicked, plays audio. I have absolutely no idea what I should be putting in for the iframe url, or what it’s needed for. The image url and source url seem fairly straightforward, although I’m a little unclear what format my audio needs to be in to be played. (m4a, I assume?). If anybody could let me know what purpose the iframe serves in this situation/what information the card’s getting from it, it would be a great help.