iPhone: transfer audio from Whatsapp to Music library
Solution 1:
Hit the share button and send it to yourself via email. Then, open your mail in iPhone and it will download the song. Long press on the name of the song until it asks which application to open in.
There, you can open that song in your preferred app (but not not the iPhone music library) like i downloader, and also download it to your OC from the emails.