Start with default generated template

templates/field/file-audio.html.twig

@@ -0,0 +1,23 @@
+{#
+/**
+* @file
+* Default theme implementation to display the file entity as an audio tag.
+*
+* Available variables:
+* - attributes: An array of HTML attributes, intended to be added to the
+*   audio tag.
+* - files: And array of files to be added as sources for the audio tag. Each
+*   element is an array with the following elements:
+*   - file: The full file object.
+*   - source_attributes: An array of HTML attributes for to be added to the
+*     source tag.
+*
+* @ingroup themeable
+*/
+#}
+{{ attach_library('aaron/file') }}
+<audio {{ attributes }}>
+  {% for file in files %}
+    <source {{ file.source_attributes }} />
+  {% endfor %}
+</audio>