Use a video converter app or website
Upload the MP4 file
Select MP3 as the output format
Start the conversion
Download the MP3 file
Use VLC Media Player
Open the MP4 file in VLC
Choose Convert/Save
Select Audio – MP3 as the profile
Save the converted file
Use FFmpeg
Run a command to extract audio and convert to MP3
Use an online MP4 to MP3 converter
Upload the file
Convert and download the MP3
Use a desktop audio converter
Import the MP4
Export or save as MP3