Hello, after adding a File Upload field with an uploaded mp3 file, you can try this script in Custom HTML.

<ul class="form-fileupload-value">
<li>
<audio controls>
<source src="/jw/web/client/app/<REPLACE APP ID>/1/form/download/<REPLACE FORM ID>/<REPLACE RECORD ID>/<REPLACE MP3 FILE NAME>.mp3.?attachment=true" type="audio/mpeg">
Your browser does not support the audio element.
</audio>
</li>
</ul>