Converting an OPUS file on the fly using iOS

My apologies if you’ve already read this question in the Automators Forum but…

Riddle me this

Do you think it would be possible to create a shortcut that would take an audio file that was saved in ‘ Files ‘, (that has been sent out of WhatsApp) as a.OPUS file and then convert it to an MP4 so that it can be attached to a ‘Day One’ entry once saved back in ‘files’ or somewhere else?

I appreciate that I can find a way of converting the file on the Mac and then attaching it to Day One, but I’m interested in being able to do this on the fly when working remotely without the Mac and therefore on my chosen IOS device