M4P music is encrypted by Apple, it is DRM protected AAC file. To convert iTunes M4P to MP3, you need the audio converter that has the ability to remove DRM from iTunes M4P, then convert to MP3.
I have two suggestions:
1. Convert iTunes M4P to MP3 within iTunes
- Burn the the iTunes M4P songs onto a CD.
- When it has finished burning, enter that CD into your computer again.
- Click on “Audio CD” under “source” on the left side of your screen in iTunes.
- Then right click on the track you want to convert to an MP3.
- Select “convert to MP3”
- Once it has finished converting, copy that file to somewhere else on your computer.
- Copy it again from where you just pasted it, and paste it into your MP3 player or other music players as you like.
2. Convert iTunes M4P to MP3 with DRM Audio Converter
Add the iTunes songs to the DRM audio converter, then choose MP3 as the output, press Convert to start the M4P to MP3 conversion and it is done. It is much faster and easier.