That is incorrect. Then you have been fooled by the Windows Media Player. Because the media player recognizes the file Container as it is native. You can name the extension as .doc and it will be still recognized as mp3. Wav mp3 or ogg files are completely different. Just Google for it. But as a I can see, you all in all didn’t read the link @Anke posted.
But back to the initial question.
@AtomDeveloper once made in extension for me to convert WAV files into mp3 using the lame library. I paid him for this. He never released that Extension official. Maybe you want to ask him. It was some tricky to implement in an App, you will need to edit the apk with apk editor and will have to insert the lame library manually. This makes the app about 20mb bigger. To answer the next question: No, won’t share that extension or an demo apk 
But maybe you want to use ogg files instead of MP3. In this case I once made an extension for this . just search The Forum