i’m not an expert on this but am using some local audio. i also use some details widgets but am gradually converting to streams. on ios, autoplay is not default, in contrast, for the same tw on other systems, only iframes that are intentionally not contained in details widgets or are in open substreams will auto play. not sure why mine is behaving differently to yours, it might be system/browser specific? i am also not using divs, just bare iframes, and have the url manually inserted e.g.
20140624 makiaea <iframe height="10px" width="40px" src="music/20140624perchance - 20210729makiaea.m4a" frameborder="0"></iframe>
or for video:
latest video (silent 19s) split–screen iphone input between tiddlywiki and anki <iframe width="277px" height="600px" src="video/20210809 split screen iphone input.mp4" frameborder="0" type="video/mp4" controls></iframe>
(edit) discourse code display