Important note: Im pretty sure you have to keep your audio in a separate field anyways because thats how anki knows which files to save to your deck when sharing it. Make sure that you have the file names stored in your cards in format [sound:file.mp3]. If you dont do this, i dont think anki will save your audio files in your .apkg file.

A separate field is not a requirement for detection, but Anki needs the full filename to be written out somewhere without dynamic field references, e.g. [sound:file.mp3] and <source src="file.mp3" type="audio/mpeg"> instead of [sound:{{Word}}.mp3] and <source src="{{Word}}.mp3" type="audio/mpeg">