Mp4 to caf audio conversion is often sought by iPhone users that try to convert their ringtones (saved as .m4r) to other audio formats, for example CAF format (Apple Core Audio).
You can use Apple iTunes for Mac or Windows to convert iPhone ringtone to Apple Core Audio Format via AIFF encoder integrated to iTunes.
First to to the Edit menu ► Preferences... ► Import Settings... button ► Import using AIFF decoder ► OK button.
Then click right mouse button on your .m4r file in your iTunes library ► and select Create AIFF Version option ► Open Windows Explorer or Finder ► find the newly created .aif file and rename it to .caf, because it should be same file format.