Convert MP4 files to MP3 using To MP3 Converter:

  1. Open To MP3 Converter.
  2. In the Finder, select a few MP4 files or folders containing them.
  3. Drag files, selected in the Finder, and drop them into To MP3 Converter, to start MP4 to MP3 conversion. To MP3 Converter for Mac OS - Dropping MP4 files
  4. Click on the links in the Progress Window to access new MP3 files. To MP3 Converter for Mac OS - Accessing new MP3 files

Read More: How to convert to MP3 - Getting Started >>
Read More: Improving Drag & Drop Experience >>

Please note, MP4 files can come with the DRM protection. DRM protected audio is not supported and cannot be converted because of the App Store policies.
Read More: Input Formats >>