Change write mode from "Compose View" to "HTML View".
Anywhere in the post body, put this code:
<audio controls="">
<source src="http://docs.google.com/uc?export=open&id=<google drive file id>" type="audio/mp3"></source>
</audio>
for <google drive file id> is the ID of the audio file (.mp3) you have uploaded to google drive.
https://drive.google.com/file/d/<google drive file id>/
