Hi Matt,
I found a way by revealing <audio autoplay src={{audio base64 encoded in a tiddler or index of data-tiddler}}>
In combination with the <$press> widget at
hammerwidgets.tiddlyspot.com it's a button that plays the audio when pressing it and stops when releasing - normal buttons simply play the whole audio file
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encoding mp3 or other formats to base64 can be done in various ways
on linux terminal there's the base64 command, I think it's available on osx, too - if not then it's installable - or there are guis or online converters
Simon